1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
|
<!doctype html>
<html>
<head>
<title>LuaBridge 2.3 Reference Manual</title>
<META HTTP-EQUIV="content-type" CONTENT="text/html; charset=iso-8859-1">
<!--=========================================================================-->
<style TYPE="text/css">
body {
color: #000000 ;
background-color: #FFFFFF ;
font-family: Helvetica, Arial, sans-serif ;
text-align: justify ;
margin-right: 30px ;
margin-left: 30px ;
}
h1, h2, h3, h4 {
font-family: Verdana, Geneva, sans-serif ;
font-weight: normal ;
font-style: normal ;
}
h1 {
padding-top: 0.4em ;
padding-bottom: 0.4em ;
padding-left: 24px ;
margin-left: -24px ;
background-color: #ffe668 ;
border-radius: 8px ;
}
h2 {
padding-top: 0.4em ;
padding-bottom: 0.4em ;
padding-left: 1em ;
padding-right: 1em ;
background-color: #ffe668 ;
border-radius: 8px ;
}
h3 {
padding-left: 0.5em ;
border-left: solid #ffe668 1em ;
}
a:link {
color: #8d5c00 ;
background-color: inherit ;
text-decoration: none ;
}
a:visited {
color: #b17b26;
background-color: inherit ;
text-decoration: none ;
}
a:link:hover, a:visited:hover {
color: #8d5c00 ;
background-color: #ffe668 ;
}
a:link:active, a:visited:active {
color: inherit;
}
hr {
border: 0 ;
height: 1px ;
color: #a0a0a0 ;
background-color: #a0a0a0 ;
}
:target {
background-color: #F8F8F8 ;
padding-top: 2px ;
padding-bottom: 2px ;
padding-left: 8px;
padding-right: 8px;
border: solid #a0a0a0 2px ;
}
.footer {
color: gray ;
font-size: small ;
}
ul {
list-style-type: none ;
list-style-position: outside ;
}
ul.bullets {
list-style-type: disc ;
}
img {
border: 0;
}
table {
margin-left: 2em;
}
pre, code {
font-size: 12pt ;
}
pre {
margin-left: 2em;
}
pre.split {
padding-left: 2em;
display: table-cell ;
white-space: pre-wrap ;
vertical-align: text-top ;
padding-right: 2em;
}
pre.split + pre.split {
border-left: 1px solid #ccc;
}
</style>
</head>
<!--=========================================================================-->
<body>
<header>
<hr>
<h1>LuaBridge 2.3 Reference Manual</h1>
<hr>
</header>
<small>
Official repository is located at
<a href="https://github.com/vinniefalco/LuaBridge">https://github.com/vinniefalco/LuaBridge</a>.
<br>
Copyright © 2012 Vinnie Falco. Freely available under the terms of the
<A HREF="http://www.opensource.org/licenses/mit-license.html">MIT License</A>.
</small>
<nav>
<H2>Contents</H2>
<UL id="toc" style="padding: 0">
<LI><A href="#s1">1 - Introduction</A>
<UL>
<LI><A href="#s1.1">1.1 - Design</A>
<LI><A href="#s1.2">1.2 - Repository</A>
<LI><A href="#s1.3">1.3 - License and Credits</A>
</UL>
<P>
<LI><A href="#s2">2 - Accessing C++ from Lua</A>
<UL>
<LI><A href="#s2.1">2.1 - Namespaces</A>
<LI><A href="#s2.2">2.2 - Data, Properties, Functions, and CFunctions</A>
<LI><A href="#s2.3">2.3 - Class Objects</A>
<LI><A href="#s2.4">2.4 - Property Member Proxies</A>
<LI><A href="#s2.5">2.5 - Function Member Proxies</A>
<LI><A href="#s2.6">2.6 - Constructors</A>
<LI><A href="#s2.7">2.7 - Lua Stack</A>
<LI><A href="#s2.8">2.8 - lua_State</A>
</UL>
<p>
<LI><A href="#s3">3 - Passing Objects</A>
<UL>
<LI><A href="#s3.1">3.1 - C++ Lifetime</A>
<LI><A href="#s3.2">3.2 - Lua Lifetime</A>
<LI><A href="#s3.3">3.3 - Pointers, References, and Pass by Value</A>
<LI><A href="#s3.4">3.4 - Shared Lifetime</A>
<UL>
<LI><A href="#s3.4.1">3.4.1 - Class RefCountedObjectPtr</A>
<LI><A href="#s3.4.2">3.4.2 - Class RefCountedPtr</A>
<LI><A href="#s3.4.3">3.4.3 - User-defined Containers</A>
<LI><A href="#s3.4.4">3.4.4 - Container Constructors</A>
</UL>
<LI><A href="#s3.5">3.5 - Mixing Lifetimes</A>
<LI><A href="#s3.6">3.6 - Convenience Functions</A>
</UL>
<P>
<LI><A href="#s4">4 - Accessing Lua from C++</A>
<UL>
<LI><A href="#s4.1">4.1 - Class LuaRef</A>
<UL>
<LI><A href="#s4.1.1">4.1.1 - Type Conversions</A>
<LI><A href="#s4.1.2">4.1.2 - Visual Studio 2010, 2012</A>
</UL>
<LI><A href="#s4.2">4.2 - Table Proxies</A>
<LI><A href="#s4.3">4.3 - Calling Lua</A>
<UL>
<LI><A href="#s4.3.1">4.3.1 - Class LuaException</A>
</UL>
</uL>
<P>
<LI><A href="#s5">5 - Security</A>
</UL>
</nav>
<!--========================================================================-->
<section>
<h1>1 - <span id="s1">Introduction</span></h1>
<p>
<a href="https://github.com/vinniefalco/LuaBridge">LuaBridge</a> is a
lightweight and dependency-free library for mapping data, functions, and
classes back and forth between C++ and <a href="http://wwww.lua.org">Lua</a>,
a powerful, fast, lightweight, embeddable scripting language. LuaBridge has
been tested and works with Lua revisions starting from 5.1.5, although it
should work in any version of Lua from 5.1.0 and later. It also works
transparently with <a href="http://luajit.org/">LuaJIT</a>.
</p>
<p>
LuaBridge offers the following features:
</p>
<ul class="bullets" title="Features">
<li><a href="http://www.opensource.org/licenses/mit-license.html">MIT Licensed</a>, no usage restrictions!</li>
<li>Headers-only: No Makefile, no .cpp files, just one <code>#include</code>!</li>
<li>Simple, light, and nothing else needed (like Boost).</li>
<li>No macros, settings, or configuration scripts needed.</li>
<li>Supports different object lifetime management models.</li>
<li>Convenient, type-safe access to the Lua stack.</li>
<li>Automatic function parameter type binding.</li>
<li>Easy access to Lua objects like tables and functions.</li>
<li>Written in a clear and easy to debug style.</li>
<li>Does not require C++11.</li>
</ul>
<p>
LuaBridge is distributed as a a collection of header files. You simply add
one line, <code>#include "LuaBridge/LuaBridge.h"</code> where you want to
pass functions, classes, and variables back and forth between C++ and Lua.
There are no additional source files, no compilation settings, and no
Makefiles or IDE-specific project files. LuaBridge is easy to integrate.
</p>
<p>
C++ concepts like variables and classes are made available to Lua through a
process called <em>registration</em>. Because Lua is weakly typed, the resulting
structure is not rigid. The API is based on C++ template metaprogramming. It
contains template code to automatically generate at compile-time the various
Lua C API calls necessary to export your program's classes and functions to
the Lua environment.
</p>
<p>
To expose Lua objects to C++, a class called <code>LuaRef</code> is provided.
The implementation allows C++ code to access Lua objects such as numbers
or strings, but more importantly to access things like tables and their
values. Using this class makes idioms like calling Lua functions simple
and clean.
</p>
<!--========================================================================-->
<section>
<h2>1.1 - <span id="s1.1">Design</span></h2>
<p>
LuaBridge tries to be efficient as possible when creating the "glue" that
exposes C++ data and functions to Lua. At the same time, the code was
written with the intention that it is all as simple and clear as possible,
without resorting to obscure C++ idioms, ugly preprocessor macros, or
configuration settings. Furthermore, it is designed to be "header-only",
making it very easy to integrate into your projects.
</p>
<p>
Because LuaBridge was written with simplicity in mind there are some features
that are not available. Although it comes close to the highest possible
performance, LuaBridge is not quite the fastest,
<a href="http://code.google.com/p/oolua/">OOLua</a> slightly outperforms
LuaBridge in some tests. LuaBridge also does not try to implement every
possible feature,
<a href="http://www.rasterbar.com/products/luabind.html">LuaBind</a>
explores every corner of the C++ language (but it requires Boost).
</p>
<p>
LuaBridge does not support:
</p>
<ul class="bullets">
<li>Enumerated constants
<li>More than 8 parameters on a function or method (although this can be
increased by adding more <code>TypeListValues</code> specializations).
<li>Overloaded functions, methods, or constructors.
<li>Global variables (variables must be wrapped in a named scope).
<li>Automatic conversion between STL container types and Lua tables
(conversion can be enabled for <code>std::list</code>, <code>std::vector</code>,
<code>std::map</code> or <code>std::unordered_map</code> by including
<code>List.h</code>, <code>Vector.h</code>, <code>Map</code> or
<code>UnorderedMap.h</code> respectively)
<li>Inheriting Lua classes from C++ classes.
<li>Passing nil to a C++ function that expects a pointer or reference.
<li>Standard containers like <code>std::shared_ptr</code>.
</ul>
</section>
<!--========================================================================-->
<section>
<h2>1.2 - <span id="s1.2">Repository</span></h2>
<p>
The official repository is located at
<a href="https://github.com/vinniefalco/LuaBridge">https://github.com/vinniefalco/LuaBridge</a>.
The branches are organized as follows:
</p>
<table>
<tr>
<td><b>master</b></td>
<td>Tagged, stable release versions.</td>
</tr>
<tr>
<td><b>release</b></td>
<td>A temporarily created branch that holds a release candidate for review.</td>
</tr>
<tr>
<td><b>develop</b></td>
<td>Contains work in progress, possibly unfinished or with bugs.</td>
</tr>
</table>
<p>
These repositories are also available:
</p>
<table>
<tr>
<td><b><a href="https://github.com/vinniefalco/LuaBridgeUnitTests">LuaBridgeUnitTests</a></b></td>
<td>A stand alone command line application to exercise LuaBridge functionality.</td>
</tr>
<tr>
<td><b><a href="https://github.com/vinniefalco/LuaBridgeDemo">LuaBridgeUnitDemo</a></b></td>
<td>A stand alone GUI application that provides an interactive console.</td>
</tr>
</table>
</section>
<!--========================================================================-->
<section>
<h2>1.3 - <span id="s1.3">License and Credits</span></h2>
<p>
LuaBridge is published under the terms of the
<a href="http://www.opensource.org/licenses/mit-license.html">MIT License</a>:
</p>
<pre>
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
</pre>
<p>
The original version of LuaBridge was written by Nathan Reed. The project
has been taken over by Vinnie Falco, who added new functionality and wrote
the new documentation. Vinnie also incorporated <code>LuaRef</code> and
other Lua to C++ binding contributions from Nigel Atkinson.
</p>
<p>
For questions, comments, or bug reports feel free to open a Github issue
or contact Vinnie Falco directly at the email address indicated below.
</p>
<ul>
<li>Copyright 2019, Dmitry Tarakanov</li>
<li>Copyright 2012, Vinnie Falco <a href="mailto:vinnie.falco@gmail.com"><vinnie.falco@gmail.com></a>
<li>Copyright 2008, Nigel Atkinson <a href="mailto:suprapilot+LuaCode@gmail.com"><suprapilot+LuaCode@gmail.com></a>
<li>Copyright 2007, Nathan Reed
<li>Portions from The Loki Library: Copyright 2001 by Andrei Alexandrescu
</ul>
<p>
Older versions of LuaBridge up to and including 0.2 (available separately) are
distributed under the BSD 3-Clause License. See the corresponding license file
in those versions (distributed separately) for more details.
</p>
</section>
<!--========================================================================-->
</section>
<section>
<h1>2 - <span id="s2">Accessing C++ from Lua</span></h1>
<p>
In order to expose C++ data and functions to Lua, each piece of exported
information must be <em>registered</em>. There are five types of objects that
LuaBridge can register:
</p>
<table>
<tr>
<td><b>Namespaces</b> </td>
<td>A Lua table that contains other registrations.</td>
</tr>
<tr>
<td><b>Data</b> </td>
<td>Global or static variables, data members, and static data members.</td>
</tr>
<tr>
<td><b>Functions </b></td>
<td>Regular functions, member functions, and static member functions.</td>
</tr>
<tr>
<td><b>CFunctions </b></td>
<td>A regular function, member function, or static member function that
uses the <code>lua_CFunction</code> calling convention.</td>
</tr>
<tr>
<td><b>Properties </b></td>
<td>Global properties, property members, and static property members.
These appear like data to Lua, but are implemented in C++ using
functions to get and set the values.</td>
</tr>
</table>
<p>
Both data and properties can be marked as <em>read-only</em> at the time of
registration. This is different from <code>const</code>; the values of these
objects can be modified on the C++ side, but Lua scripts cannot change them.
Code samples that follow are in C++ or Lua, depending on context. For brevity
of exposition code samples in C++ assume the traditional variable
<code>lua_State* L</code> is defined, and that a <code>using namespace luabridge</code>
using-directive is in effect.
</p>
<!--========================================================================-->
<section>
<h2>2.1 - <span id="s2.1">Namespaces</span></h2>
<p>
All LuaBridge registrations take place in a <em>namespace</em>. When we refer
to a <em>namespace</em> we are always talking about a namespace in the Lua
sense, which is implemented using tables. The namespace need not correspond
to a C++ namespace; in fact no C++ namespaces need to exist at all unless you
want them to. LuaBridge namespaces are visible only to Lua scripts; they are
used as a logical grouping tool. To obtain access to the global namespace
we write:
</p>
<pre>
getGlobalNamespace (L);
</pre>
<p>
This returns an object on which further registrations can be performed. The
subsequent registrations will go into the global namespace, a practice which
is not recommended. Instead, we can add our own namespace by writing:
</p>
<pre>
getGlobalNamespace (L)
.beginNamespace ("test");
</pre>
<p>
This creates a table in <code>_G</code> called "test". Since we have not
performed any registrations, this table will be empty except for some
bookkeeping key/value pairs. LuaBridge reserves all identifiers that start
with a double underscore. So <code>__test</code> would be an invalid name
(although LuaBridge will silently accept it). Functions like
<code>beginNamespace</code> return the corresponding object on which we can
make more registrations. Given:
</p>
<pre>
getGlobalNamespace (L)
.beginNamespace ("test")
.beginNamespace ("detail")
.endNamespace ()
.beginNamespace ("utility")
.endNamespace ()
.endNamespace ();
</pre>
<p>
The results are accessible to Lua as <code>test</code>, <code>test.detail</code>,
and <code>test.utility</code>. Here we introduce the <code>endNamespace</code>
function; it returns an object representing the original enclosing namespace.
All LuaBridge functions which create registrations return an object upon which
subsequent registrations can be made, allowing for an unlimited number of
registrations to be chained together using the dot operator. Adding two objects
with the same name, in the same namespace, results in undefined behavior
(although LuaBridge will silently accept it).
</p>
<p>
A namespace can be re-opened later to add more functions. This lets you split
up the registration between different source files. These are equivalent:
</p>
<pre>
getGlobalNamespace (L)
.beginNamespace ("test")
.addFunction ("foo", foo)
.endNamespace ();
getGlobalNamespace (L)
.beginNamespace ("test")
.addFunction ("bar", bar)
.endNamespace ();
</pre>
<p>
and
</p>
<pre>
getGlobalNamespace (L)
.beginNamespace ("test")
.addFunction ("foo", foo)
.addFunction ("bar", bar)
.endNamespace ();
</pre>
</section>
<!--========================================================================-->
<section>
<h2>2.2 - <span id="s2.2">Properties and Functions</span></h2>
<p>
These are registered into a namespace using <code>addProperty</code>
and <code>addFunction</code>.
When registered functions are called by scripts, LuaBridge automatically takes
care of the conversion of arguments into the appropriate data type when doing
so is possible. This automated system works for the function's return value,
and up to 8 parameters although more can be added by extending the templates.
Pointers, references, and objects of class type as parameters are treated
specially, and explained later.
</p>
<p>
If we have:
</p>
<pre>
int globalVar;
static float staticVar;
std::string stringProperty;
std::string getString () { return stringProperty; }
void setString (std::string s) { stringProperty = s; }
int foo () { return 42; }
void bar (char const*) { }
int cFunc (lua_State* L) { return 0; }
</pre>
<p>
These are registered with:
</p>
<pre>
getGlobalNamespace (L)
.beginNamespace ("test")
.addProperty ("var1", &globalVar)
.addProperty ("var2", &staticVar, false) // read-only
.addProperty ("prop1", getString, setString)
.addProperty ("prop2", getString) // read only
.addFunction ("foo", foo)
.addFunction ("bar", bar)
.addFunction ("cfunc", cFunc)
.endNamespace ();
</pre>
<p>
Variables can be marked <em>read-only</em> by passing <code>false</code> in
the second optional parameter. If the parameter is omitted, <em>true</em> is
used making the variable read/write. Properties are marked read-only by
omitting the set function. After the registrations above, the following Lua
identifiers are valid:
</p>
<pre>
test -- a namespace
test.var1 -- a lua_Number property
test.var2 -- a read-only lua_Number property
test.prop1 -- a lua_String property
test.prop2 -- a read-only lua_String property
test.foo -- a function returning a lua_Number
test.bar -- a function taking a lua_String as a parameter
test.cfunc -- a function with a variable argument list and multi-return
</pre>
<p>
Note that <code>test.prop1</code> and <code>test.prop2</code> both refer to the
same value. However, since <code>test.prop2</code> is read-only, assignment
attempts will generate a run-time error. These Lua statements have the stated effects:
</p>
<pre>
test.var1 = 5 -- okay
test.var2 = 6 -- error: var2 is not writable
test.prop1 = "Hello" -- okay
test.prop1 = 68 -- okay, Lua converts the number to a string
test.prop2 = "bar" -- error: prop2 is not writable
test.foo () -- calls foo and discards the return value
test.var1 = foo () -- calls foo and stores the result in var1
test.bar ("Employee") -- calls bar with a string
test.bar (test) -- error: bar expects a string not a table
</pre>
<p>
LuaBridge does not support overloaded functions nor is it likely to in the
future. Since Lua is dynamically typed, any system that tries to resolve a set
of parameters passed from a script will face considerable ambiguity when
trying to choose an appropriately matching C++ function signature.
</p>
</section>
<!--========================================================================-->
<section>
<h2>2.3 - <span id="s2.3">Class Objects</span></h2>
<p>
A class registration is opened using either <code>beginClass</code> or
<code>deriveClass</code> and ended using <code>endClass</code>. Once
registered, a class can later be re-opened for more registrations using
<code>beginClass</code>. However, <code>deriveClass</code> should only be
used once. To add more registrations to an already registered derived class,
use <code>beginClass</code> on it.
</p>
<p>
These declarations:
</p>
<pre>
struct A {
static int staticData;
static float staticProperty;
static float getStaticProperty () { return staticProperty; }
static void setStaticProperty (float f) { staticProperty = f; }
static void staticFunc () { }
static int staticCFunc (lua_State *L) { return 0; }
std::string dataMember;
char dataProperty;
char getProperty () const { return dataProperty; }
void setProperty (char v) { dataProperty = v; }
std::string toString () const { return dataMember; }
void func1 () { }
virtual void virtualFunc () { }
int cfunc (lua_State* L) { return 0; }
};
struct B : public A {
double dataMember2;
void func1 () { }
void func2 () { }
void virtualFunc () { }
};
int A::staticData;
float A::staticProperty;
</pre>
<p>
are registered using:
</p>
<pre>
getGlobalNamespace (L)
.beginNamespace ("test")
.beginClass <A> ("A")
.addStaticProperty ("staticData", &A::staticData)
.addStaticProperty ("staticProperty", &A::getStaticProperty, &A::setStaticProperty)
.addStaticFunction ("staticFunc", &A::staticFunc)
.addStaticFunction ("staticCFunc", &A::staticCFunc)
.addProperty ("data", &A::dataMember)
.addProperty ("prop", &A::getProperty, &A::setProperty)
.addFunction ("func1", &A::func1)
.addFunction ("virtualFunc", &A::virtualFunc)
.addFunction ("__tostring", &A::toString) // Metamethod
.addFunction ("cfunc", &A::cfunc)
.endClass ()
.deriveClass <B, A> ("B")
.addProperty ("data", &B::dataMember2)
.addFunction ("func1", &B::func1)
.addFunction ("func2", &B::func2)
.endClass ()
.endNameSpace ();
</pre>
<p>
Method registration works just like function registration. Virtual methods
work normally; no special syntax is needed. const methods are detected and
const-correctness is enforced, so if a function returns a const object (or
a container holding to a const object) to Lua, that reference to the object
will be considered const and only const methods can be called on it.
It is possible to register Lua metamethods (except <code>__gc</code>).
Destructors are registered automatically for each class.
</p>
<p>
As with regular variables and properties, class properties can be
marked read-only by passing false in the second parameter, or omitting the set
set function. The <code>deriveClass</code> takes two template arguments: the
class to be registered, and its base class. Inherited methods do not have to
be re-declared and will function normally in Lua. If a class has a base class
that is **not** registered with Lua, there is no need to declare it as a
subclass.
</p>
<p>
Remember that in Lua, the colon operator '<code>:</code>' is used for
method call syntax:
</p>
<pre>
local a = A ()
a.func1 () -- error: func1 expects an object of a registered class
a.func1 (a) -- okay, verbose, this how OOP works in Lua
a:func1 () -- okay, less verbose, equvalent to the previous
</pre>
</section>
<!--========================================================================-->
<section>
<h2>2.4 - <span id="s2.4">Property Member Proxies</span></h2>
<p>
Sometimes when registering a class which comes from a third party library, the
data is not exposed in a way that can be expressed as a pointer to member,
there are no get or set functions, or the get and set functons do not have the
right function signature. Since the class declaration is closed for changes,
LuaBridge allows for a <em>property member proxy</em>. This is a pair of get
and set flat functions which take as their first parameter a pointer to
the object. This is easily understood with the following example:
</p>
<pre>
// Third party declaration, can't be changed
struct Vec
{
float coord [3];
};
</pre>
<p>
Taking the address of an array element, e.g. <code>&Vec::coord [0]</code>
results in an error instead of a pointer-to-member. The class is closed for
modifications, but we want to export Vec objects to Lua using the familiar
object notation. To do this, first we add a "helper" class:
</p>
<pre>
struct VecHelper
{
template <unsigned index>
static float get (Vec const* vec)
{
return vec->coord [index];
}
template <unsigned index>
static void set (Vec* vec, float value)
{
vec->coord [index] = value;
}
};
</pre>
<p>
This helper class is only used to provide property member proxies.
<code>Vec</code> continues to be used in the C++ code as it was before.
Now we can register the <code>Vec</code> class with property member proxies for
<code>x</code>, <code>y</code>, and <code>z</code>:
</p>
<pre>
getGlobalNamespace (L)
.beginNamespace ("test")
.beginClass <Vec> ("Vec")
.addProperty ("x", &VecHelper::get <0>, &VecHelper::set <0>)
.addProperty ("y", &VecHelper::get <1>, &VecHelper::set <1>)
.addProperty ("z", &VecHelper::get <2>, &VecHelper::set <2>)
.endClass ()
.endNamespace ();
</pre>
<p>
With a C++11 compilant compiler it is possible to use <code>std::function</code>
instances as proxies:
</p>
<pre>
getGlobalNamespace (L)
.beginNamespace ("test")
.beginClass <Vec> ("Vec")
.addProperty ("x",
std::function <float (const Vec*)> (
[] (const Vec* vec) {return vec->coord [0];}),
std::function <void (Vec*, float)> (
[] (Vec* vec, float v) {vec->coord [0] = v;}))
// ... same for "y" and "z"
.endClass ()
.endNamespace ();
</pre>
</section>
<!--========================================================================-->
<section>
<h2>2.5 - <span id="s2.5">Function Member Proxies</span></h2>
<p>
Where it is not possible or inconvenient to add a member to be registered,
LuaBridge also allows for a <em>function member proxy</em>. This is a flat
function which take as its first parameter a pointer to the object:
</p>
<pre>
// Third party declaration, can't be changed
struct Vec
{
float coord [3];
};
</pre>
<p>
The class is closed for modifications, but we want to extend Vec objects
with our member function. To do this, first we add a "helper" function:
</p>
<pre>
void scale (float value)
{
value->coord [0] *= value;
value->coord [1] *= value;
value->coord [2] *= value;
};
</pre>
<p>
Now we can register the <code>Vec</code> class with a member function
<code>scale</code>:
</p>
<pre>
getGlobalNamespace (L)
.beginNamespace ("test")
.beginClass <Vec> ("Vec")
.addFunction ("scale", &scale)
.endClass ()
.endNamespace ();
</pre>
<p>
With a C++11 compilant compiler it is possible to use <code>std::function</code>
instances as proxies:
</p>
<pre>
getGlobalNamespace (L)
.beginClass <Vec> ("Vec")
.addFunction ("scaleX",
std::function <void (Vec*, float)> (
[] (Vec* vec, float v) {vec->coord [0] *= v;}))
.endClass ()
</pre>
</section>
<!--========================================================================-->
<section>
<h2>2.6 - <span id="s2.6">Constructors</span></h2>
<p>
A single constructor may be added for a class using <code>addConstructor</code>.
LuaBridge cannot automatically determine the number and types of constructor
parameters like it can for functions and methods, so you must provide them.
This is done by specifying the signature of the desired constructor function
as the first template parameter to <code>addConstructor</code>. The parameter
types will be extracted from this (the return type is ignored). For example,
these statements register constructors for the given classes:
</p>
<pre>
struct A {
A ();
};
struct B {
explicit B (char const* s, int nChars);
};
getGlobalNamespace (L)
.beginNamespace ("test")
.beginClass <A> ("A")
.addConstructor <void (*) (void)> ()
.endClass ()
.beginClass <B> ("B")
.addConstructor <void (*) (char const*, int)> ()
.endClass ()
.endNamespace ();
</pre>
<p>
Constructors added in this fashion are called from Lua using the fully
qualified name of the class. This Lua code will create instances of
<code>A</code> and <code>B</code>.
</p>
<pre>
a = test.A () -- Create a new A.
b = test.B ("hello", 5) -- Create a new B.
b = test.B () -- Error: expected string in argument 1
</pre>
</section>
<!--========================================================================-->
<section>
<h2>2.7 - <span id="s2.7">Lua Stack</span></h2>
<p>
In the Lua C API, all operations on the <code>lua_State</code> are performed
through the Lua stack. In order to pass values back and forth between C++
and Lua, LuaBridge uses specializations of this template class concept:
</p>
<pre>
template <class T>
struct Stack
{
static void push (lua_State* L, T t);
static T get (lua_State* L, int index);
};
</pre>
<p>
When a specialization of <code>Stack</code> exists for a given type
<code>T</code> we say that the <code>T</code> is <em>convertible</em>.
Throughout this document and the LuaBridge API, these types can be used
anywhere a convertible type is expected.
</p>
<p>
The Stack template class specializations are used automatically for variables,
properties, data members, property members, function arguments and return
values. These basic types are supported:
</p>
<ul class="bullets">
<li><code>bool</code>
<li><code>char</code>, converted to a string of length one.
<li><code>char const*</code> and <code>std::string</code> strings.
<li>Integers, <code>float</code>, and <code>double</code>,
converted to <code>Lua_number</code>.
</ul>
<p>
User-defined types which are convertible to one of the basic types are
possible, simply provide a <code>Stack<></code> specialization in the
<code>luabridge</code> namespace for your user-defined type, modeled after
the existing types. For example, here is a specialization for a
<code>juce::String</code>:
</p>
<pre>
template <>
struct Stack <juce::String>
{
static void push (lua_State* L, juce::String s)
{
lua_pushstring (L, s.toUTF8 ());
}
static juce::String get (lua_State* L, int index)
{
return juce::String (luaL_checkstring (L, index));
}
};
</pre>
</section>
<!--========================================================================-->
<section>
<h2>2.8 - <span id="s2.8">lua_State</span></h2>
<p>
Sometimes it is convenient from within a bound function or member function
to gain access to the <code>lua_State*</code> normally available to a </code>lua_CFunction</code>.
With LuaBridge, all you need to do is add a <code>lua_State*</code> as the last
parameter of your bound function:
</p>
<pre>
void useState (lua_State* L);
getGlobalNamespace (L).addFunction ("useState", &useState);
</pre>
<p>
You can still include regular arguments while receiving the state:
</p>
<pre>
void useStateAndArgs (int i, std::string s, lua_State* L);
getGlobalNamespace (L).addFunction ("useStateAndArgs", &useStateAndArgs);
</pre>
<p>
When the script calls <code>useStateAndArgs</code>, it passes only the integer
and string parameters. LuaBridge takes care of inserting the <code>lua_State*</code>
into the argument list for the corresponding C++ function. This will work
correctly even for the state created by coroutines. Undefined behavior results
if the <code>lua_State*</code> is not the last parameter.
</p>
<p>
The same is applicable for properies.
</p>
</section>
<!--========================================================================-->
</section>
<section>
<h1>3 - <span id="s3">Passing Objects</span></h1>
<p>
An object of a registered class <code>T</code> may be passed to Lua as:
</p>
<table>
<tr>
<td><b><code>T</code></b></td>
<td>Passed by value (a copy), with <em>Lua lifetime</em>.</td>
</tr>
<tr>
<td><b><code>T const</code></b></td>
<td>Passed by value (a copy), with <em>Lua lifetime</em>.</td>
</tr>
<tr>
<td><b><code>T*</code></b></td>
<td>Passed by reference, with <em>C++ lifetime</em>.</td>
</tr>
<tr>
<td><b><code>T&</code></b></td>
<td>Passed by reference, with <em>C++ lifetime</em>.</td>
</tr>
<tr>
<td><b><code>T const*</code></b></td>
<td>Passed by const reference, with <em>C++ lifetime</em>.</td>
</tr>
<tr>
<td><b><code>T const&</code></b></td>
<td>Passed by const reference, with <em>C++ lifetime</em>.</td>
</tr>
</table>
<!--========================================================================-->
<section>
<h2>3.1 - <span id="s3.1">C++ Lifetime</span></h2>
<p>
The creation and deletion of objects with <em>C++ lifetime</em> is controlled by
the C++ code. Lua does nothing when it garbage collects a reference to such an
object. Specifically, the object's destructor is not called (since C++ owns
it). Care must be taken to ensure that objects with C++ lifetime are not
deleted while still being referenced by a <code>lua_State*</code>, or else
undefined behavior results. In the previous examples, an instance of <code>A</code>
can be passed to Lua with C++ lifetime, like this:
</p>
<pre>
A a;
push (L, &a); // pointer to 'a', C++ lifetime
lua_setglobal (L, "a");
push (L, (A const*)&a); // pointer to 'a const', C++ lifetime
lua_setglobal (L, "ac");
push <A const*> (L, &a); // equivalent to push (L, (A const*)&a)
lua_setglobal (L, "ac2");
push (L, new A); // compiles, but will leak memory
lua_setglobal (L, "ap");
</pre>
</section>
<!--========================================================================-->
<section>
<h2>3.2 - <span id="s3.2">Lua Lifetime</span></h2>
<p>
When an object of a registered class is passed by value to Lua, it will have
<em>Lua lifetime</em>. A copy of the passed object is constructed inside the
userdata. When Lua has no more references to the object, it becomes eligible
for garbage collection. When the userdata is collected, the destructor for
the class will be called on the object. Care must be taken to ensure that
objects with Lua lifetime are not accessed by C++ after they are garbage
collected, or else undefined behavior results. An instance of <code>B</code>
can be passed to Lua with Lua lifetime this way:
</p>
<pre>
B b;
push (L, b); // Copy of b passed, Lua lifetime.
lua_setglobal (L, "b");
</pre>
<p>
Given the previous code segments, these Lua statements are applicable:
</p>
<pre>
print (test.A.staticData) -- Prints the static data member.
print (test.A.staticProperty) -- Prints the static property member.
test.A.staticFunc () -- Calls the static method.
print (a.data) -- Prints the data member.
print (a.prop) -- Prints the property member.
a:func1 () -- Calls A::func1 ().
test.A.func1 (a) -- Equivalent to a:func1 ().
test.A.func1 ("hello") -- Error: "hello" is not a class A.
a:virtualFunc () -- Calls A::virtualFunc ().
print (b.data) -- Prints B::dataMember.
print (b.prop) -- Prints inherited property member.
b:func1 () -- Calls B::func1 ().
b:func2 () -- Calls B::func2 ().
test.B.func2 (a) -- Error: a is not a class B.
test.A.func1 (b) -- Calls A::func1 ().
b:virtualFunc () -- Calls B::virtualFunc ().
test.B.virtualFunc (b) -- Calls B::virtualFunc ().
test.A.virtualFunc (b) -- Calls B::virtualFunc ().
test.B.virtualFunc (a) -- Error: a is not a class B.
a = nil; collectgarbage () -- 'a' still exists in C++.
b = nil; collectgarbage () -- Lua calls ~B() on the copy of b.
</pre>
<p>
When Lua script creates an object of class type using a registered
constructor, the resulting value will have Lua lifetime. After Lua no longer
references the object, it becomes eligible for garbage collection. You can
still pass these to C++, either by reference or by value. If passed by
reference, the usual warnings apply about accessing the reference later,
after it has been garbage collected.
</p>
</section>
<!--========================================================================-->
<section>
<h2>3.3 - <span id="s3.3">Pointers, References, and Pass by Value</span></h2>
<p>
When C++ objects are passed from Lua back to C++ as arguments to functions,
or set as data members, LuaBridge does its best to automate the conversion.
Using the previous definitions, the following functions may be registered
to Lua:
</p>
<pre>
void func0 (A a);
void func1 (A* a);
void func2 (A const* a);
void func3 (A& a);
void func4 (A const& a);
</pre>
<p>
Executing this Lua code will have the prescribed effect:
</p>
<pre>
func0 (a) -- Passes a copy of a, using A's copy constructor.
func1 (a) -- Passes a pointer to a.
func2 (a) -- Passes a pointer to a const a.
func3 (a) -- Passes a reference to a.
func4 (a) -- Passes a reference to a const a.
</pre>
<p>
In the example above, all functions can read the data members and property
members of <code>a</code>, or call const member functions of <code>a</code>.
Only <code>func0</code>, <code>func1</code>, and <code>func3</code> can
modify the data members and data properties, or call non-const member
functions of <code>a</code>.
</p>
<p>
The usual C++ inheritance and pointer assignment rules apply. Given:
</p>
<pre>
void func5 (B b);
void func6 (B* b);
</pre>
<p>
These Lua statements hold:
</p>
<pre>
func5 (b) - Passes a copy of b, using B's copy constructor.
func6 (b) - Passes a pointer to b.
func6 (a) - Error: Pointer to B expected.
func1 (b) - Okay, b is a subclass of a.
</pre>
<p>
When a pointer or pointer to const is passed to Lua and the pointer is null
(zero), LuaBridge will pass Lua a <code>nil</code> instead. When Lua passes a
<code>nil</code> to C++ where a pointer is expected, a null (zero) is passed
instead. Attempting to pass a null pointer to a C++ function expecting a
reference results in <code>lua_error</code> being called.
</p>
</section>
<!--========================================================================-->
<section>
<h2>3.4 - <span id="s3.4">Shared Lifetime</span></h2>
<p>
LuaBridge supports a <em>shared lifetime</em> model: dynamically allocated
and reference counted objects whose ownership is shared by both Lua and C++.
The object remains in existence until there are no remaining C++ or Lua
references, and Lua performs its usual garbage collection cycle. A container
is recognized by a specialization of the <code>ContainerTraits</code>
template class. LuaBridge will automatically recognize when a data type is
a container when the correspoding specialization is present. Two styles of
containers come with LuaBridge, including the necessary specializations.
</p>
<!--========================================================================-->
<section>
<h3>3.4.1 - <span id="s3.4.1">Class RefCountedObjectPtr</span></h3>
<p>
This is an intrusive style container. Your existing class declaration must be
changed to be also derived from <code>RefCountedObject</code>. Given
<code>class T</code>, derived from <code>RefCountedObject</code>, the container
<code>RefCountedObjectPtr <T></code> may be used. In order for
reference counts to be maintained properly, all C++ code must store a
container instead of the pointer. This is similar in style to
<code>std::shared_ptr</code> although there are slight differences. For
example:
</p>
<pre>
// A is reference counted.
struct A : public RefCountedObject
{
void foo () { }
};
struct B
{
RefCountedObjectPtr <A> a; // holds a reference to A
};
void bar (RefCountedObjectPtr <A> a)
{
a->foo ();
}
</pre>
</section>
<!--========================================================================-->
<section>
<h3>3.4.2 - <span id="s3.4.2">Class RefCountedPtr</span></h3>
<p>
This is a non intrusive reference counted pointer. The reference counts are
kept in a global hash table, which does incur a small performance penalty.
However, it does not require changing any already existing class declarations.
This is especially useful when the classes to be registered come from a third
party library and cannot be modified. To use it, simply wrap all pointers
to class objects with the container instead:
</p>
<pre>
struct A
{
void foo () { }
};
struct B
{
RefCountedPtr <A> a;
};
RefCountedPtr <A> createA ()
{
return new A;
}
void bar (RefCountedPtr <A> a)
{
a->foo ();
}
void callFoo ()
{
bar (createA ());
// The created A will be destroyed
// when we leave this scope
}
</pre>
</section>
<!--========================================================================-->
<section>
<h3>3.4.3 - <span id="s3.4.3">User-defined Containers</span></h3>
<p>
If you have your own container, you must provide a specialization of
<code>ContainerTraits</code> in the <code>luabridge</code> namespace for your
type before it will be recognized by LuaBridge (or else the code will not
compile):
</p>
<pre>
template <class T>
struct ContainerTraits <CustomContainer <T> >
{
typedef typename T Type;
static T* get (CustomContainer <T> const& c)
{
return c.getPointerToObject ();
}
};
</pre>
<p>
Standard containers like <code>std::shared_ptr</code> or
<code>boost::shared_ptr</code> <b>will not work</b>. This is because of type
erasure; when the object goes from C++ to Lua and back to C++, there is no
way to associate the object with the original container. The new container is
constructed from a pointer to the object instead of an existing container.
The result is undefined behavior since there are now two sets of reference
counts.
</p>
</section>
<!--========================================================================-->
<section>
<h3>3.4.4 - <span id="s3.4.4">Container Constructors</span></h3>
<p>
When a constructor is registered for a class, there is an additional
optional second template parameter describing the type of container to use.
If this parameter is specified, calls to the constructor will create the
object dynamically, via operator new, and place it a container of that
type. The container must have been previously specialized in
<code>ContainerTraits</code>, or else a compile error will result. This code
will register two objects, each using a constructor that creates an object
with Lua lifetime using the specified container:
</p>
<pre>
class C : public RefCountedObject
{
C () { }
};
class D
{
D () { }
};
getGlobalNamespace (L)
.beginNamespace ("test")
.beginClass <C> ("C")
.addConstructor <void (*) (void), RefCountedObjectPtr <C> > ()
.endClass ()
.beginClass <D> ("D")
.addConstructor <void (*) (void), RefCountedPtr <D> > ()
.endClass ();
.endNamespace ()
</pre>
</section>
<!--========================================================================-->
</section>
<section>
<h2>3.5 - <span id="s3.5">Mixing Lifetimes</span></h2>
<p>
Mixing object lifetime models is entirely possible, subject to the usual
caveats of holding references to objects which could get deleted. For
example, C++ can be called from Lua with a pointer to an object of class
type; the function can modify the object or call non-const data members.
These modifications are visible to Lua (since they both refer to the same
object). An object store in a container can be passed to a function expecting
a pointer. These conversion work seamlessly.
<p>
</section>
<!--========================================================================-->
<section>
<h2>3.6 - <span id="s3.6">Convenience Functions</span></h2>
<p>
The <code>setGlobal</code> function can be used to assign any convertible
value into a global variable.
</p>
</section>
<!--========================================================================-->
</section>
<section>
<h1>4 - <span id="s4">Accessing Lua from C++</span></h1>
<p>
Because Lua is a <em>dynamically typed language</em>, special consideration
is required to map values in Lua to C++. The following sections describe the
classes and functions used for representing Lua types. Only the essential
operations are explained; To gain understanding of all available functions,
please refer to the documentation comments in the corresponding source files.
</p>
<!--========================================================================-->
<section>
<h2>4.1 - <span id="s4.1">Class LuaRef</span></h2>
<p>
The <code>LuaRef</code> class is a container which references any Lua type.
It can hold anything which a Lua variable can hold: <strong>nil</strong>,
number, boolean, string, table, function, thread, userdata, and
lightuserdata. Because <code>LuaRef</code> uses the <code>Stack</code>
template specializations to do its work, classes, functions, and data
exported to Lua through namespace registrations can also be stored (these
are instances of userdata). In general, a <code>LuaRef</code> can represent
any <em>convertible</em> C++ type as well as all Lua types.
</p>
<p>
A <code>LuaRef</code> variable constructed with no parameters produces a
reference to <strong>nil</strong>:
</p>
<pre>
LuaRef v (L); // References nil
</pre>
<p>
To construct a <code>LuaRef</code> to a specific value, the two parameter
constructor is used:
</p>
<pre>
LuaRef v1 (L, 1); // A LUA_TNUMBER
LuaRef v2 (L, 1.1); // Also a LUA_TNUMBER
LuaRef v3 (L, true); // A LUA_TBOOLEAN
LuaRef v4 (L, "string"); // A LUA_TSTRING
</pre>
<p>
The functions <code>newTable</code> and <code>getGlobal</code> create
references to new empty table and an existing value in the global table
respectively:
</p>
<pre>
LuaRef v1 = newTable (L); // Create a new table
LuaRef v2 = getGlobal (L, "print") // Reference to _G ["print"]
</pre>
<p>
A <code>LuaRef</code> can hold classes <em>registered</em> using LuaBridge:
</p>
<pre>
class A;
//...
LuaRef v (L, new A); // A LuaBridge userdata holding a pointer to A
</pre>
<p>
Any convertible type may be assigned to an already-existing <code>LuaRef</code>:
</p>
<pre>
LuaRef v (L); // Nil
v = newTable (L); // An empty table
v = "string" // A string. The prevous value becomes
// eligible for garbage collection.
</pre>
<p>
A <code>LuaRef</code> is itself a convertible type, and the convertible
type <code>Nil</code> can be used to represent a Lua <strong>nil</strong>.
</p>
<pre>
LuaRef v1 (L, "x"); // assign "x"
LuaRef v2 (L, "y"); // assign "y"
v2 = v1; // v2 becomes "x"
v1 = "z"; // v1 becomes "z", v2 is unchanged
v1 = newTable (L); // An empty table
v2 = v1; // v2 references the same table as v1
v1 = Nil (); // v1 becomes nil, table is still
// referenced by v2.
</pre>
<p>
Values stored in a <code>LuaRef</code> object obey the same rules as
variables in Lua: tables, functions, threads, and full userdata values are
<em>objects</em>. The <code>LuaRef</code> does not actually <em>contain</em>
these values, only <em>references</em> to them. Assignment, parameter
passing, and function returns always manipulate references to such values;
these operations do not imply any kind of copy.
</p>
<!--========================================================================-->
<section>
<h3>4.1.1 - <span id="s4.1.1">Type Conversions</span></h3>
<p>
A universal C++ conversion operator is provided for implicit conversions
which allow a <code>LuaRef</code> to be used where any convertible type is
expected. These operations will all compile:
</p>
<pre>
void passInt (int);
void passBool (bool);
void passString (std::string);
void passObject (A*);
LuaRef v (L);
//...
passInt (v); // implicit conversion to int
passBool (v); // implicit conversion to bool
passString (v); // implicit conversion to string
passObject (v); // must hold a registered LuaBridge class or a
// lua_error() will be called.
</pre>
<p>
Since Lua types are dynamic, the conversion is performed at run time using
traditional functions like <code>lua_toboolean</code> or
<code>lua_tostring</code>. In some cases, the type information may be
incorrect especially when passing objects of registered class types.
When performing these conversions, LuaBridge may raise a Lua error by
directly or indirectly calling <code>lua_error</code> To be bullet-proof,
such code must either be wrapped in a <code>lua_pcall</code>, or you must
install a Lua <em>panic function</em> that throws an exception which you
can catch.
</p>
<p>
When an explicit conversion is required (such as when writing templates),
use the <code>cast</code> template function or an explicit C++ style cast.
</p>
<pre>
void passString (std::string);
LuaRef v (L);
// The following are all equivalent:
passString (std::string (v));
passString ((std::string)v);
passString (static_cast <std::string> (v));
passString (v.cast <std::string> ());
</pre>
</section>
<!--========================================================================-->
<section>
<h3>4.1.2 - <span id="s4.1.2">Visual Studio 2010, 2012</span></h3>
<p>
There is a defect with all versions of Visual Studio up to and including
Visual Studio 2012 which prevents the implicit conversion operator from
being applied when it is used as an operand in a boolean operator:
</p>
<pre>
LuaRef v1 (L);
LuaRef v2 (L);
if (v1 || v2) { } // Compile error in Visual Studio
// Work-arounds:
if (v1.cast <bool> () || v2.cast <bool> ()) { }
if (bool (v1) || bool (v2)) { }
</pre>
</section>
<!--========================================================================-->
</section>
<section>
<h2>4.2 - <span id="s4.2">Table Proxies</span></h2>
<p>
As tables are the sole data structuring mechanism in Lua, the
<code>LuaRef</code> class provides robust facilities for accessing and
manipulating table elements using a simple, precise syntax. Any convertible
type may be used as a key or value. Applying the array indexing operator
<code>[]</code> to a <code>LuaRef</code> returns a special temporary object
called a <em>table proxy</em> which supports all the operations which can
be performed on a <code>LuaRef</code>. In addition, assignments made to
table proxies change the underlying table. Because table proxies are
compiler-created temporary objects, you don't work with them directly. A
LuaBridge table proxy should not be confused with the Lua proxy table
technique described in the book "Programming in Lua"; the LuaBridge table
proxy is simply an intermediate C++ class object that works behind the
scenes to make table manipulation syntax conform to C++ idioms. These
operations all invoke table proxies:
</p>
<pre>
LuaRef v (L);
v = newTable (L);
v ["name"] = "John Doe"; // string key, string value
v [1] = 200; // integer key, integer value
v [2] = newTable (L); // integer key, LuaRef value
v [3] = v [1]; // assign 200 to integer index 3
v [1] = 100; // v[1] is 100, v[3] is still 200
v [3] = v [2]; // v[2] and v[3] reference the same table
v [2] = Nil (); // Removes the value with key = 2. The table
// is still referenced by v[3].
</pre>
</section>
<!--========================================================================-->
<section>
<h2>4.3 - <span id="s4.3">Calling Lua</span></h2>
<p>
Table proxies and <code>LuaRef</code> objects provide a convenient syntax
for invoking <code>lua_pcall</code> on suitable referenced object. This
includes C functions, Lua functions, or Lua objects with an appropriate
<code>__call</code> metamethod set. The provided implementation supports
up to eight parameters (although more can be supported by adding new
functions). Any convertible C++ type can be passed as a parameter in its
native format. The return value of the function call is provided as a
<code>LuaRef</code>, which may be <strong>nil</strong>.
</p>
<pre class="split">
LuaRef same = getGlobal (L, "same");
// These all evaluate to true
same (1,1);
!same (1,2);
same ("text", "text");
!same (1, "text");
same (1, 1, 2); // third param ignored
</pre>
<pre class="split">
function same (arg1, arg)
return arg1 == arg2
end
</pre>
<p>
Table proxies support all of the Lua call notation that <code>LuaRef</code>
supports, making these statements possible:
</p>
<pre class="split">
LuaRef v = getGlobal (L, "t");
t[1]();
t[2]("a", "b");
t[2](t[1]); // Call t[3] with the value in t[2]
t[4]=t[3](); // Call t[3] and store the result in t[4].
t [t[5]()] = "wow"; // Store "wow" at the key returned by
// the call to t[5]
</pre>
<pre class="split">
t = {}
t[1] = function () print ("hello") end
t[2] = function (u, v) print (u, v) end
t[3] = "foo"
</pre>
<!--========================================================================-->
<h3>4.3.1 - <span id="s4.3.1">Class LuaException</span></h3>
<section >
<p>
When <code>LuaRef</code> is used to call into Lua using the <code>()</code>
operator it issues a protected call using <code>lua_pcall</code>. LuaBridge
uses the C++ exception handling mechanism, throwing a <code>LuaException</code>
object:
</p>
<pre class="split">
LuaRef f (L) = getGlobal (L, "fail");
try {
f ();
}
catch (LuaException const& e) {
std::cerr && e.what ();
}
</pre>
<pre class="split">
function fail ()
error ("A problem occurred")
end
</pre>
</section>
<!--========================================================================-->
</section>
<!--========================================================================-->
</section>
<section>
<h1>5 - <span id="s5">Security</span></h1>
<p>
The metatables and userdata that LuaBridge creates in the <code>lua_State*</code> are
protected using a security system, to eliminate the possibility of undefined
behavior resulting from scripted manipulation of the environment. The
security system has these components:
</p>
<ul class="bullets">
<li>
Class and const class tables use the <em>table proxy</em> technique. The
corresponding metatables have <code>__index</code> and <code>__newindex</code>
metamethods, so these class tables are immutable from Lua.
<li>
Metatables have <code>__metatable</code> set to a boolean value. Scripts
cannot obtain the metatable from a LuaBridge object.
<li>
Classes are mapped to metatables through the registry, which Lua scripts
cannot access. The global environment does not expose metatables
<li>
Metatables created by LuaBridge are tagged with a lightuserdata key which
is unique in the process. Other libraries cannot forge a LuaBridge
metatable.
</ul>
<p>
This security system can be easily bypassed if scripts are given access to
the debug library (or functionality similar to it, i.e. a raw <code>getmetatable</code>).
The security system can also be defeated by C code in the host, either by
revealing the unique lightuserdata key to another module or by putting a
LuaBridge metatable in a place that can be accessed by scripts.
</p>
<p>
When a class member function is called, or class property member accessed,
the <code>this</code> pointer is type-checked. This is because member functions exposed
to Lua are just plain functions that usually get called with the Lua colon
notation, which passes the object in question as the first parameter. Lua's
dynamic typing makes this type-checking mandatory to prevent undefined
behavior resulting from improper use.
</p>
<p>
If a type check error occurs, LuaBridge uses the <code>lua_error</code>
mechanism to trigger a failure. A host program can always recover from
an error through the use of <code>lua_pcall</code>; proper usage of
LuaBridge will never result in undefined behavior.
</p>
</section>
<!--========================================================================-->
</body>
</html>
|
