On 7/2/2012 7:26 PM, Ravi wrote:
On Monday, July 02, 2012 12:41:22 PM Eric Niebler wrote:
Use of a C++11 feature just for the sake of it doesn't seem like such a good idea to me.
<baffle> Have I not given enough good reasons above? Maybe I'll just keep my good ideas to myself next time. :-/
Please don't. This one is actually pretty widely applicable if you are doing type deduction in C++11; it took me quite a while to figure this one out when I ran into it. I, too, fail to see how the reasons you gave were not perfectly clear.
Thanks Ravi. For the record, this trick is also useful for CRTP bases when you need to static_cast this from base to derived in a return type: template<typename Derived> struct Base { template<typename D = Derived> auto foo() -> decltype(static_cast<D *>(this)->bar()) { return static_cast<D *>(this)->bar(); } }; struct Derived : Base<Derived> { int bar() { return 0; } }; int main() { Derived d; d.foo(); } If you try to do this instead: auto foo() -> decltype(static_cast<Derived *>(this)->bar()) it won't compile because the compiler can't tell that the static_cast is legit. You might think this would work: auto foo() -> decltype(std::declval<Derived &>().bar()) ...but then it can't find member bar() in Derived. -- Eric Niebler BoostPro Computing http://www.boostpro.com