Allocator Part of Type

[jmh530]

On Thursday, 15 March 2018 at 21:43:41 UTC, Steven Schveighoffer 
wrote:
> [snip]
> I don't know if I've heard Andrei talk about that, but I 
> definitely have made it part of the type for types that need to 
> allocate. The only other possibility is to accept and use an 
> Allocator object (i.e. the interface).
>
> I suppose the main reason you may want to not make it part of 
> the type is if you want to compare/assign two types built with 
> different allocators. But then I don't know why you would want 
> to do that.
>
> But I just thought of this too -- maybe he said you should make 
> it a part of the struct itself? That is, you shouldn't make the 
> allocator a member, but the allocator itself can be part of the 
> type?
>
> Not sure.
>
> -Steve

I first remember him saying it with respect to C++'s allocators 
[1]. The C++ containers in std include the allocator as part of 
the type. I don't really recall what the reasoning was. I also 
recall him saying it with respect to automem [2].

Automem includes the allocator among the template variables and 
then puts the allocator in an enum (Atila says it only takes up 
space in certain situations). I think the containers library does 
something similar, but with an alias if state size is 0 and as a 
member otherwise.



[1] 
https://github.com/CppCon/CppCon2015/blob/master/Presentations/allocator%20Is%20to%20Allocation%20what%20vector%20Is%20to%20Vexation/allocator%20Is%20to%20Allocation%20what%20vector%20Is%20to%20Vexation%20-%20Andrei%20Alexandrescu%20-%20CppCon%202015.pdf

[2] https://forum.dlang.org/post/ocden9$11s6$1@digitalmars.com