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And, by extending your second example, we can enforce the minimum array size with std::enable_if (C++11; boost::enable_if_c with C++03): template <size_t N
by pyrtsa 14y ago
And, by extending your second example, we can enforce the minimum array size with std::enable_if (C++11; boost::enable_if_c with C++03):
template <size_t N>
typename enable_if<(N >= 10), void>::type
foo(int (&bar)[N]) { ... }
EDIT: Changed condition from N >= 0 into a more meaningful one. X-)
- huhtenberg 14y ago... and just as I was going to make a smart-ass joke about Boost probably having another contrived contraption just for that - there it is, already sneaked into the standard too.
- pbsd 14y agoThe more readable C++11 version would use static_assert: template <size_t N> foo(int (&bar)[N]) { static_assert(N >= 10, "Array needs >= 10 elements!"); ... }
- pyrtsa 14y agoCorrect. The key difference is that the enable_if version can be overloaded with mutually exclusive requirements: template <size_t N> typename enable_if<(1 < N && N < 10), void>::type foo(int (&bar)[N]) { // called when 1 < N && N < 10 } template <size_t N> typename enable_if<(N >= 10), void>::type foo(int (&bar)[N]) { // called when N >= 10 } OTOH, the key advantage in static_assert is the meaningful error message.
- abcd_f 14y agoThis will generate separate function bodies for different values of N.
- zokier 14y agoI don't think that is more readable. With enable_if the precondition is clearly visible at the function header, while the static_assert is inside the body and thus more easily accidentally ignored.
- obiterdictum 14y agoOn the other hand, static_assert will have a more helpful compile error for users of the code. They will clearly see assertion condition that failed, rather than missing candidate error due to substitution failure (or worse, a different overload silently considered instead).