On Thu, Jan 22, 2015 at 6:49 PM, TONGARI J
You're right, I misunderstood the situation.
Your code doesn't work for clang, it seems to be more strict than g++: "error: a lambda expression may not appear inside of a constant expression" I suspect it's also a bug, since a hand-written functor does compile.
Hmm, this might be the problem, but I'm still not sure if this is a compiler bug or not. According to the standard, the type of the object yielded by a lambda expression has an implicitly declared default constructor/copy constructor/destructor as they are for any other type, and since the type is stateless, that would mean that those operations are constexpr. I don't mind that operator() isn't constexpr because I never actually use it as such. I suppose that if someone were to be pedantic, they could argue that even though all of the constructors are constexpr, the object still might not necessarily be a constant expression. Still, I'm not certain that the omission of such a detail would imply that the object isn't a constant expression. I think the standard may have just unintentionally left this unspecified, in which case it would be valid for a compiler to accept this code or for a compiler to deny the code. -- -Matt Calabrese