On Monday, September 20, 2010 18:21:53 Jesse Phillips wrote: > bearophile Wrote: > > - C Standard says that assigning to one member of a union and then > > accessing a different member is undefined behaviour. - GCC is a > > practical compiler, so it has the -fno-strict-aliasing switch, that > > allows to use that trick. See "-Wstrict-aliasing" and: > > http://stackoverflow.com/questions/2906365/gcc-strict-aliasing-and-casti > > ng-through-a-union - Walter said that regarding such union semantics D > > acts as C. So that union trick will break with other future D compilers. > > I believe that defined behavior within an area where C is specified to be > undefined is completely in line with operating as C does. But where does > Walter say Unions act as C in this case? Why not, define the behavior and > leave it.
Well, since C doesn't define the behavior, D can do anything - including using behavior that it defines and considers entirely consistent. So, as long as it's D code, I see no reason why D can't use the same constructs as C code but have things which are undefined in C be defined in D. The only problem is if you port code from D to C, but that's not exactly something that we're generally worried about. Overall though, I get the impression that Walter's goal is to get as close to having no undefined behavior in D as he reasonably can. Whether the behavior is defined in another language or not isn't particularly relevant. - Jonathan M Davis
