What's the use case? I'm trying to think of a situation where you'd want to do that were you might not just make a separate binary that uses the other allocator
Custom allocators are extremely common in C and C++ code, and often improve performance over general purpose allocators (though they can also make things worse if you're not careful).
The C++ STL has custom allocators (though the initial design was sort of botched; there is a new polymorphic allocator mechanism that aims to fix it IIRC)
Zig's docs cover a few different scenarios, but a couple of interest to me at least:
- Arena allocators, where your code allocates a chunk of memory and then creates its own allocator just for that chunk; when that chunk gets freed, so does everything in it. Handy for short-lived data.
- Using different allocators for different regions of memory makes it trivial to compartmentalize things; you could use the OS allocator (or a straight pointer if you're implementing your own OS) to preallocate chunks of memory, slap allocators on those chunks, and hand those to different components, preventing any given component from bringing down the whole program due to a memory leak.
- It's possible to use allocators for verifying code correctness (e.g. detecting memory leaks, testing code under memory exhaustion conditions, etc.).
