Pseudo properties using macros in GameMaker

Properties.gml

#macro VAR "foo"
#macro GETTER variable_global_get(VAR)
#macro SETTER \ 
        for (var __value = GETTER;; { \ 
            if (is_real(__value) && __value > 0) { \ 
                variable_global_set(VAR, __value); \ 
            } else { \ 
                show_error("Global property '" + VAR + "' must be a positive number", false); \ 
            } \ 
            break; \
        }) __value

Examples

Getting and setting:

SETTER = 12;
show_message(GETTER); // prints: '12'

Setting an invalid value:

SETTER = 1.0;    // success
SETTER = "five"; // error

Using the addition assignment operator on the property:

SETTER = 2;      // value: 2
SETTER += 5;     // value: 7

You may also be able to create a getter-setter using the macro:

#macro GETSET GETTER; SETTER

with the limitation of not being able to use it 'inline' like the original getter.

In other words, the following is invalid code:

GETSET = 3;
show_message(GETSET);         // invalid token

since the macro GETSET will be transformed into:

GETTER; SETTER = 3;
show_message(GETTER; SETTER); // invalid token

which is obviously invalid.