ClickHouse/libs/libcommon/include/ext/identity.hpp

23 lines
871 B
C++

#pragma once
namespace ext
{
/// \brief Identity function for use with other algorithms as a pass-through.
class identity
{
/** \brief Function pointer type template for converting identity to a function pointer.
* Presumably useless, provided for completeness. */
template <typename T> using function_ptr_t = T &&(*)(T &&);
/** \brief Implementation of identity as a non-instance member function for taking function pointer. */
template <typename T> static T && invoke(T && t) { return std::forward<T>(t); }
public:
/** \brief Returns the value passed as a sole argument using perfect forwarding. */
template <typename T> T && operator()(T && t) const { return std::forward<T>(t); }
/** \brief Allows conversion of identity instance to a function pointer. */
template <typename T> operator function_ptr_t<T>() const { return &invoke; };
};
}