IsStreamable.hpp

// Distributed under the MIT License.
// See LICENSE.txt for details.
 
#pragma once
 
#include <type_traits>
 
#include "Utilities/Requires.hpp"
#include "Utilities/StlStreamDeclarations.hpp"
 
namespace tt {
// @{
/// \ingroup TypeTraitsGroup
/// \brief Check if type `T` has operator<<(`S`, `T`) defined.
///
/// \details
/// Inherits from std::true_type if the type `T` has operator<<(`S`, `T`)
/// defined for a stream `S`, otherwise inherits from std::false_type
///
/// \usage
/// For any type `T` and stream type `S`,
/// \code
/// using result = tt::is_streamable<S, T>;
/// \endcode
///
/// \metareturns
/// std::bool_constant
///
/// \semantics
/// If the type `T` has operator<<(`S`, `T`) defined for stream `S`, then
/// \code
/// typename result::type = std::true_type;
/// \endcode
/// otherwise
/// \code
/// typename result::type = std::false_type;
/// \endcode
///
/// \example
/// \snippet Test_IsStreamable.cpp is_streamable_example
/// \see std::cout std::ifstream std::sstream std::ostream
/// \tparam S the stream type, e.g. std::stringstream or std::ostream
/// \tparam T the type we want to know if it has operator<<
template <typename S, typename T, typename = std::void_t<>>
struct is_streamable : std::false_type {};
 
/// \cond
template <typename S, typename T>
struct is_streamable<
    S, T,
    std::void_t<decltype(std::declval<std::add_lvalue_reference_t<S>>()
                         << std::declval<T>()),
                Requires<not std::is_same<S, T>::value>>> : std::true_type {};
/// \endcond
 
/// \see is_streamable
template <typename S, typename T>
constexpr bool is_streamable_v = is_streamable<S, T>::value;
 
/// \see is_streamable
template <typename S, typename T>
using is_streamable_t = typename is_streamable<S, T>::type;
// @}
}  // namespace tt