>In a completely manually managed language like C or C++, you can handle fragmentation problems yourself by writing your own allocators or doing object pools to reuse previously allocated memory. You have control over fragmentation.

It's done constantly in Rust. Create a vector of items you want to allocate. Reference to them by their id, i.e. int representing them. There're libraries supporting this style of development, for example, slab: https://crates.io/crates/slab