Variant macros

Many macros that are used in module definitions have variants with an additional _P suffix. These variants always take a single additional argument, of type int *. When the module is imported and before calling Main, a numeric identifier is stored in that location that can be used to refer to the defined entity efficiently. The pointer argument must point to a global variable defined in the current compilation unit. The _P macro variants behave otherwise identically to the ordinary macros.

Example

The _P variant macros are provided for convenience and efficiency reasons. For example, they can be used to access data related to a global definition more efficiently than by using the name of the definition. Consider this implementation of a trivial function that returns the value of a global variable:

static AValue GetValue(AThread *t, AValue *frame)
{
    return AGlobal(t, "example::Variable");
}

A_MODULE(example, "example")
    A_VAR("Variable")
    A_DEF("GetValue", 0, 0, GetValue)
A_END_MODULE()

The function GetValue can be implemented more efficiently with the help of a A_VAR_P macro:

static int VariableNum;

static AValue GetValue(AThread *t, AValue *frame)
{
    return AGlobalByNum(VariableNum);
}

A_MODULE(example, "example")
    A_VAR_P("Variable", &VariableNum)
    A_DEF("GetValue", 0, 0, GetValue)
A_END_MODULE()

The potentially costly call to AGlobal in GetValue was replaced with the much faster AGlobalByNum call. It should be noted that the same effect can be achieved, though not as elegantly, by defining a Main function for the module and initializing VariableNum in this function using AGetGlobalNum.

Variant macros for global definitions

The following variant macros are available for global definitions:

• A_DEF_P
• A_DEF_OPT_P
• A_DEF_VARARGS_P
• A_VAR_P
• A_EMPTY_CONST_P
• A_SYMBOLIC_CONST_P
• A_CLASS_P
• A_CLASS_PRIV_P

The numeric identifier initialized by these macros can be used to access the defined global value using AGlobalByNum and ASetGlobalByNum.

Variant macros for member definitions

The following variant macros are available for member definitions within class definitions:

• A_VAR_P
• A_EMPTY_CONST_P

In these cases, the stored numeric identifier refers to the physical member slot that can be accessed using AMemberDirect and ASetMemberDirect. Read the descriptions of these functions carefully, since using these functions can be dangerous!

Variant macro A_BINARY_DATA_P

The A_BINARY_DATA_P variant stores the binary data offset that can be used as an argument for ADataPtr, ASetData_M and AGetData_M.