memcpy() comparison: C, Rust, and D

[Walter Bright via Digitalmars-d]

On 2/1/2017 6:39 AM, Cody Laeder wrote:
> The _traditional_ C-like memcpy [3] in the stdlib. It is unsafe, and carries no
> side effects for the src buffer. It enforces type safety, but it cannot enforce
> memory safety as you can blow past the allocation side on your dst buffer (hence
> why it is unsafe).

It also does not guarantee the function does not save a copy of those pointers 
and dereference them later.

Programmers "know" this to be true for memcpy, but the compiler cannot know this 
from the Rust (or C) declaration. The D version does present this guarantee by 
annotating it with 'pure'.

This matters because such a saved pointer can become a dangling reference - a 
memory corruption bug waiting to happen.

[Note: in Rust, functions marked 'unsafe' may store copies of their arguments in 
globals. 'safe' functions may not access mutable global storage.]