Phobos 3 Discussion Notes - 02-01-2024

[Paul Backus]

On Wednesday, 7 February 2024 at 11:46:11 UTC, Richard (Rikki) 
Andrew Cattermole wrote:
> My conclusion was that you really only have two use cases for 
> composable allocators:
>
> 1. You know about memory patterns, locking, type sizes ext. Use 
> composable directly.
> 2. Otherwise, use virtual.
>
> There doesn't seem to be anything in between.

The relevant constraint here isn't composability, it's safety.

In order to make allocators @safe (which is the goal of my 
proposal), you have to guarantee somehow that memory blocks can 
only be deallocated by the same allocator that originally 
allocated them.

It is possible to do this with a polymorphic allocator, but it 
incurs an enormous amount of runtime overhead, which rules out 
making it the default approach.

Of course, if you don't care about @safe, you can ignore all of 
this and use a much simpler design. Personally, I think Phobos V3 
should support @safe as much as possible, but ultimately that 
choice is up to project leadership.