Add in constant variants for invalid refs. #16293

What is the problem this request aims to solve?

Currently in order to mark an asset or data structure as "invalid", one must assign a different value to a variable that contains that data structure. Which does work fine, mostly. However GameMaker has a rather awful history of mixing different variable types together.

• -1
• noone
• undefined
• pointer_null

The problem is further increased when most *_exists functions do allow undefined, but vertex_buffer_exists() and vertex_format_exists() don't. So people end up forced to mix n matching types.

Likewise, it would be nice if refs had a proper invalid handle to reference from. Alrea
dy this is possible to do in GameMaker via a macro, but it is not a compile-time constant.

#macro handle_surface_null (handle_parse("ref surface -1"))

How do you suggest we solve this problem?

Adding native constants that directly store a "ref surface -1" and similar would allow quick easy assignments without making the game do extra work for it.

This means it is possible to do

surface_free(surf);
surf = handle_surface_null;

ds_grid_destroy(grid);
grid = handle_grid_null;

buffer_delete(buffer);
buffer = handle_buffer_null;

Are there any alternative ways to solve this problem you want to suggest?

The macro above already works "as is", it's just not compile-time.