[musl] Re: realloci(): A realloc() variant that works in-place

[Florian Weimer]

* Paul Eggert:

> On 10/31/25 10:22, Alejandro Colomar wrote:
>> Paul, for context, this is a discussion for adding a function
>> 
>> 	int realloci(void *p, size_t n);
>> 
>> that changes the size of a memory block without moving it.  (And thus,
>> fails rather often, for some implementations of allocators.)
>
> Reading the threads leading into this, the motivation for this seems to 
> be C++ and similar memory allocators that want a cheap way to grow an 
> object - if the object doesn't move they can skip some reinitialization 
> work, otherwise they have more work to do.
>
> With that in mind, the proposed API is not the best way to go about the 
> problem. What these users want is a function that acts just like 
> R=realloc(P,N) EXCEPT that it lets you compare R==P, and if the two 
> values are the same pointer you know the object did not move and you can 
> skip some work. This is simpler than realloci because it means that you 
> need only one call (not two) in the common case when realloci returns 
> the null pointer.

This would not help C++ because C++ doesn't have this kind of in-place
adjust-all-pointers operation.  There's just copy and move, and both
need non-overlapping old and new storage at the same time.