if¶
Header¶
#include <boost/hof/if.hpp>
Description¶
The if_ function decorator makes the function callable if the boolean
condition is true. The if_c version can be used to give a boolean
condition directly(instead of relying on an integral constant).
When if_ is false, the function is not callable. It is a subtitution
failure to call the function.
Synopsis¶
template<class IntegralConstant>
constexpr auto if_(IntegralConstant);
template<bool B, class F>
constexpr auto if_c(F);
Requirements¶
IntegralConstant must be:
- IntegralConstant
F must be:
- ConstInvocable
- MoveConstructible
Example¶
#include <boost/hof.hpp>
#include <cassert>
struct sum_f
{
template<class T>
int operator()(T x, T y) const
{
return boost::hof::first_of(
boost::hof::if_(std::is_integral<T>())(boost::hof::_ + boost::hof::_),
boost::hof::always(0)
)(x, y);
}
};
int main() {
assert(sum_f()(1, 2) == 3);
assert(sum_f()("", "") == 0);
}