Vision for the D language - stabilizing complexity?

[sarn via Digitalmars-d]

On Wednesday, 13 July 2016 at 10:02:58 UTC, Ola Fosheim Grøstad 
wrote:
> «Undefined» simply means that such code is not part of the 
> specified language, as in, it is no longer the language 
> covered. The optimizer is an implementation detail, the 
> optimizer is not allowed to change the semantics of the 
> language.
>
> If casting away immutable is claimed to be undefined behaviour 
> it simply means that code that does this is not in the language 
> and the compiler could refuse to compile such code if it was 
> capable of detecting it. Or it _could_ specify it to have a 
> specific type of semantics, but that would be a new language.

You're confusing "undefined" with "implementation defined".

Implementation-defined stuff is something that's not specified, 
but can be presumed to do *something*.  Undefined stuff is 
something that's officially considered to not even make sense, so 
a compiler can assume it never happens (even though a programmer 
can make the mistake of letting it happen).  This is sometimes 
controversial, but does let optimisers do some extra tricks with 
sane code.