\begin{note}

This allows types without a \tcode{value} static data member

to be template arguments for \tcode{conjunction}, as long as an

earlier argument evaluates to \tcode{false}, for example:

\begin{codeblock}

template<class T>

concept HasValue = requires { { T::value } -> std::convertible_to<bool>; };

template<class T>

using maybe_value = std::conjunction<std::bool_constant<HasValue<T>>, T>;

struct X { };

static_assert( ! maybe_value<X>::value ); // OK, \tcode{X::value} not used

static_assert( ! maybe_value<int>::value ); // OK, \tcode{int::value} not used

static_assert( maybe_value<std::true_type>::value );

\end{codeblock}

\end{note}