D equivalent of C++ reinterpret cast?

[Ali Çehreli]

Jonathan M Davis wrote:
 > On Sunday 19 September 2010 17:07:38 bearophile wrote:
 >> orgoton baberek:
 >>> Use a union, which is the correct and safe way.
 >> C standard say that's not safe. You can force that to be safe in 
C-GCC if
 >> you explicitly disable a compiler optimization. I think D docs don't say
 >> anything about this. And Walter has said that regarding such things 
D acts
 >> as C. So I am not sure that will be safe in future D.
 >>
 >> Bye,
 >> bearophile
 >
 > I'd have to go digging in old posts, but I'm pretty sure that that's 
essentially
 > how you're supposed to do it in D. I haven't ever done it because I 
think that
 > that sort of casting is pretty evil and only should be used as a last 
resort,
 > but I believe that unions are the correct way to handle it in D.

I remember being a part of a discussion where D'is unions were told to 
be exactly the same as C's. That means, results of using a union is only 
specified when it's used through one its members. Writing to one member 
and reading from another is unspecified. It is clear that endianness and 
padding should complicate matters.

But it's still used in C in low level code. That must be because 
programs are not as portable as thought; and if they are, compile time 
checks and macro magic are possible to obtain expected behavior.

Ali