http://d.puremagic.com/issues/show_bug.cgi?id=9087
--- Comment #7 from bearophile_h...@eml.cc 2012-11-28 14:17:31 PST --- (In reply to comment #6) Thank you for your answers, Jonathan. > And why should we take a performance hit with a required copy I think you are missing something. If you use "ref" or "const ref" no copy is performed: // program#4 struct S { int x; } void main() { auto items = [S(1), S(2), S(3)]; foreach (ref it; items) it.x++; } In program#3 there was a copy because in that case the programmer do wants a copy. > Honestly, I don't think that I have _ever_ seen a bug caused by this. Assuming you have understood what's the bug-class I am talking about (and I am not sure of this, given what I think is the above mistake of yours), yours is only one data point. Mine is another data point, and in my code the unwanted modification of a struct in a foreach loop has caused me several bugs. And in the D newsgroup some other persons have said they make mistakes about this. Another important data point is the design of C#, that in the case discussed in this enhancement request disallows mutation. So in the end it's quite more one person against your case. > That doesn't mean that it can't happen or that it hasn't happened, but I don't > think that it's even vaguely worth worrying about. It seems to be a common enough situation that's recognized as bug prone. So it's worth worrying about, because this class of problems is not hard to prevent. > You have a habit of trying to get warnings created for every > single stray mistake that you think a programmer might make, I agree that raising a warning here is a suboptimal solution. I think the right solution is to do something more similar to C#, and disallow the struct mutation in foreach unless you put a "ref" tag. The total number of warnings I am asking for in Bugzilla is really small, probably around 3-4. > There comes a point where you have > to let the programmer do their job and assume that they're not going to be an > idiot. We are *very* far from that in D, for a D programmer there are plenty of things to take care of to write correct programs :-) -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------