> This only works for very specific use cases, like a fixed server size where you know exactly how much memory you want to allocate to a process.

So, like, the JVM with its "initial heap size" setting? After reserving that space from the OS on startup, pieces of the space are then handed out by the JVM's internal allocator, where and when needed.

If initial heap size and max heap size are the same, that initial one is the only malloc() call that ever happens. Not as common for desktop software, but a common best practice when deploying JVM applications to servers.

(I think we're perhaps tripping over two different meanings of "allocate" - you can "allocate" in the sense of calling malloc(), and you can "allocate" a piece of that reserved memory to a particular scope/function/object without actually calling malloc.)

> Allocating memory as needed isn’t a Rust-specific idiom.

I never said that.