# Change Log

## 2013-08-22 - Remove `boost::signal` and switch to `Simple::Signal`.

According to the [benchmarks](http://timj.testbit.eu/2013/cpp11-signal-system-performance/) Simple::Signal is an order of magnitude faster than `boost::signal`. Additionally, `boost::signal` is now deprecated in favor of `boost::signal2`, which is not supported on versions of Boost on a number of platforms.

This is an implementation detail and should not affect EntityX users at all.

## 2013-08-18 - Destroying an entity invalidates all other references

Previously, `Entity::Id` was a simple integer index (slot) into vectors in the `EntityManager`. EntityX also maintains a list of deleted entity slots that are reused when new entities are created. This reduces the size and frequency of vector reallocation. The downside though, was that if a slot was reused, entity IDs referencing the entity before reallocation would be invalidated on reuse.

Each slot now also has a version number and a "valid" bit associated with it. When an entity is allocated the version is incremented and the valid bit set. When an entity is destroyed, the valid bit is cleared. `Entity::Id` now contains all of this information and can correctly determine if an ID is still valid across destroy/create.

## 2013-08-17 - Python scripting, and a more robust build system

Two big changes in this release:

1. Python scripting support (alpha).
    - Bridges the EntityX entity-component system into Python.
    - Components and entities can both be defined in Python.
    - Systems must still be defined in C++, for performance reasons.

    Note that there is one major design difference between the Python ECS model and the C++ model: entities in Python can receive and handle events.
 
    See the [README](https://github.com/alecthomas/entityx/blob/master/entityx/python/README.md) for help, and the [C++](https://github.com/alecthomas/entityx/blob/master/entityx/python/PythonSystem_test.cc) and [Python](https://github.com/alecthomas/entityx/tree/master/entityx/python/entityx/tests) test source for more examples.

2. Made the build system much more robust, including automatic feature selection with manual override.