repeat_while

Header

#include <boost/hof/repeat_while.hpp>

Description

The repeat_while function decorator will repeatedly apply a function while the predicate returns a boolean that is true. If the predicate returns an IntergralConstant then the predicate is only evaluated at compile-time.

Synopsis

template<class Predicate>
constexpr auto repeat_while(Predicate predicate);

Requirements

Predicate must be:

• ConstFunctionObject
• MoveConstructible

Example

#include <boost/hof.hpp>
#include <cassert>

struct increment
{
    template<class T>
    constexpr std::integral_constant<int, T::value + 1> operator()(T) const
    {
        return std::integral_constant<int, T::value + 1>();
    }
};

struct not_6
{
    template<class T>
    constexpr std::integral_constant<bool, (T::value != 6)> 
    operator()(T) const
    {
        return std::integral_constant<bool, (T::value != 6)>();
    }
};

typedef std::integral_constant<int, 1> one;
typedef std::integral_constant<int, 6> six;

int main() {
    auto increment_until_6 = boost::hof::repeat_while(not_6())(increment());
    static_assert(std::is_same<six, decltype(increment_until_6(one()))>::value, "Error");
}