On 09/19/13 20:01, Ivan Kazmenko wrote: > On Thursday, 19 September 2013 at 07:45:44 UTC, monarch_dodra wrote: >> On Thursday, 19 September 2013 at 06:39:09 UTC, Ivan Kazmenko wrote: >>> On Thursday, 19 September 2013 at 01:41:15 UTC, mrd wrote: >>>> Why argument "value" in contract isn't equal 2 ? >>> Why should it be? <snip> >> I actually disagree though: How the function is implemented should have no >> bearing on how the output contract should be implemented. Both should get >> their own copy of the args. The implementation of a function should not have >> to create a local duplicate just because it happens to know that it has an >> out contract. >> >> This is particularly relent since (in theory), an in/out contract should >> appear in a function's interface, and compiled/called by client code (though >> that's not the case today). > > That doesn't seem to be possible in every case. For example, what if an > argument is a class with copy constructor disabled?
In general, the problem is with accessing the argument at all, it could indeed be uncopyable, but it could also be invalid /after/ the body of the function is executed. Eg void f(ref S s) out { assert(s.x==42); } body { free(&s); } Anything that either invalidates or moves ownership can easily result in invalid accesses. Variations on this could use pointers, classes, s/free/send/, refcounts etc (and having to always clear every stale ref isn't a practical solution). > I'm not claiming that the current behavior is the best one. I just don't get > a coherent picture of how it could be defined otherwise. And the current > definition seems to follow the principle of least surprise for me. out-contracts shouldn't have access to the input args by default; that is something that should be explicitly requested. Some syntax sugar, for the cases when it actually is needed, could be nice, yes. But it's not how D currently defines out contracts, so that would be a larger change than just fixing the leak (which isn't a big problem in itself, the implications of speccing it like that would be). artur