AngelScript: Registering a value type

# Registering a value type

When registering a value type, the size of the type must be given so that AngelScript knows how much space is needed for it. If the type doesn't require any special treatment, i.e. doesn't contain any pointers or other resource references that must be maintained, then the type can be registered with the flag asOBJ_POD. In this case AngelScript doesn't require the default constructor, assignment behaviour, or destructor as it will be able to automatically handle these cases the same way it handles built-in primitives.

If you plan on passing the or returning the type by value to registered functions that uses native calling convention, you also need to inform how the type is implemented in the application, but if you only plan on using generic calling conventions, or don't pass these types by value then you don't need to worry about that.

    // Register a primitive type, that doesn't need any special management of the content
    r = engine->RegisterObjectType("pod", sizeof(pod), asOBJ_VALUE | asOBJ_POD); assert( r >= 0 );

    // Register a class that must be properly initialized and uninitialized
    r = engine->RegisterObjectType("val", sizeof(val), asOBJ_VALUE); assert( r >= 0 );

See also:
  The string object (STL) or vector3 add-on for examples of value types

## Constructor and destructor

If a constructor or destructor is needed they shall be registered the following way:

    void Constructor(void *memory)
    {
      // Initialize the pre-allocated memory by calling the
      // object constructor with the placement-new operator
      new(memory) Object();
    }

    void Destructor(void *memory)
    {
      // Uninitialize the memory by calling the object destructor
      ((Object*)memory)->~Object();
    }

    // Register the behaviours
    r = engine->RegisterObjectBehaviour("val", asBEHAVE_CONSTRUCT, "void f()", asFUNCTION(Constructor), asCALL_CDECL_OBJLAST); assert( r >= 0 );
    r = engine->RegisterObjectBehaviour("val", asBEHAVE_DESTRUCT, "void f()", asFUNCTION(Destructor), asCALL_CDECL_OBJLAST); assert( r >= 0 );

## Value types and native calling conventions

If the type will be passed to and from the application by value using native calling conventions, it is important to inform AngelScript of its real type in C++, otherwise AngelScript won't be able to determine exactly how C++ is treating the type in a parameter or return value.

There are a few different flags for this:

asOBJ_APP_CLASS | The C++ type is a class, struct, or union
asOBJ_APP_CLASS_CONSTRUCTOR | The C++ type has a defined constructor
asOBJ_APP_CLASS_DESTRUCTOR | The C++ type has a defined destructor
asOBJ_APP_CLASS_ASSIGNMENT | The C++ type has a defined assignment operator
asOBJ_APP_PRIMITIVE | The C++ type is a C++ primitive, but not a float or double
asOBJ_APP_FLOAT | The C++ type is a float or double

Note that these don't represent how the type will behave in the script language, only what the real type is in the host application. So if you want to register a C++ class that you want to behave as a primitive type in the script language you should still use the flag asOBJ_APP_CLASS. The same thing for the flags to identify that the class has a constructor, destructor, or assignment. These flags tell AngelScript that the class has the respective function, but not that the type in the script language should have these behaviours.

For class types there are also a shorter form of the flags for each combination of the 4 flags. They are of the form asOBJ_APP_CLASS_CDA, where the existance of the last letters determine if the constructor, destructor, and/or assignment behaviour are available. For example asOBJ_APP_CLASS_CDA is defined as asOBJ_APP_CLASS | asOBJ_APP_CLASS_CONSTRUCTOR | asOBJ_APP_CLASS_DESTRUCTOR | asOBJ_APP_CLASS_ASSIGNMENT.

    // Register a complex type that will be passed by value to the application
    r = engine->RegisterObjectType("complex", sizeof(complex), asOBJ_VALUE | asOBJ_APP_CLASS_CDA); assert( r >= 0 );

Make sure you inform these flags correctly, because if you do not you may get various errors when executing the scripts. Common problems are stack corruptions, and invalid memory accesses. In some cases you may face more silent errors that may be difficult to detect, e.g. the function is not returning the expected values.