SYS_CallIf.h

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/*
 * PROPRIETARY INFORMATION.  This software is proprietary to
 * Side Effects Software Inc., and is not to be reproduced,
 * transmitted, or disclosed in any way without written permission.
 *
 * NAME:        SYS_TypeTraits.h (SYS Library, C++)
 *
 * COMMENTS:    Wrapper for Boost.TypeTraits
 */

#ifndef __SYS_CALLIF_H_INCLUDED__
#define __SYS_CALLIF_H_INCLUDED__

/// @file

#include "SYS_Compiler.h"
#include "SYS_Deprecated.h"
#include "SYS_Inline.h"

#include <utility>

#if SYS_HAS_CXX14
  #define SYS_CALLIF_AUTO auto
#else
  #define SYS_CALLIF_AUTO 
#endif

#if defined(__clang__) || !defined(_MSC_VER) || _MSC_VER >= 1930
  #define SYS_CALLIF_DEPRECATED SYS_DEPRECATED_REPLACE(20.0, "if constexpr")
#else
  #define SYS_CALLIF_DEPRECATED 
#endif

/// This is replaced by 'if constexpr' in C++17.
///
/// This function is for use with lambdas to force the compiler to
/// not even try compiling or inlining function calls when a compile-time
/// condition is false.
///
/// Usage: SYS_CallIf<CONDITION>::call([&](SYS_CALLIF_AUTO) { ... });
///
/// @note Your lambda must have exactly 1 parameter of type SYS_CALLIF_AUTO
/// @{
template<bool CONDITION>
struct SYS_CallIf
{
    template<typename FUNCTOR, typename... ARGS>
    SYS_CALLIF_DEPRECATED
    static SYS_FORCE_INLINE void call(FUNCTOR functor, ARGS&&... args)
    {
        // No call at all if CONDITION is false
    }
};

template<>
struct SYS_CallIf<true>
{
#if SYS_HAS_CXX14
    template<typename FUNCTOR, typename... ARGS>
    SYS_CALLIF_DEPRECATED
    static SYS_FORCE_INLINE void call(FUNCTOR functor, ARGS&&... args)
    {
        struct dummy {};
        functor(dummy(), std::forward<ARGS>(args)...);
    }
#else
    template<typename FUNCTOR, typename... ARGS>
    SYS_CALLIF_DEPRECATED
    static SYS_FORCE_INLINE void call(FUNCTOR functor, ARGS&&... args)
    {
        functor(std::forward<ARGS>(args)...);
    }
#endif
};
/// @}

#endif // __SYS_CALLIF_H_INCLUDED__