text: /*
   * Copyright (C) 2018 Apple Inc. All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
   * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
   * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
   * THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  #pragma once
  
  #include <type_traits>
  
  namespace WTF {
  
  template<typename T>
  struct FunctionTraits;
  
  #if USE(JSVALUE32_64)
  
  template<typename T>
  static constexpr unsigned slotsForCCallArgument()
  {
      static_assert(!std::is_class<T>::value || sizeof(T) <= sizeof(void*), "This doesn't support complex structs.");
      static_assert(sizeof(T) == 8 || sizeof(T) <= 4, "");
      // This assumes that all integral values are passed on the stack.
      if (sizeof(T) == 8)
          return 2;
  
      return 1;
  }
  
  template<typename T>
  static constexpr unsigned computeCCallSlots() { return slotsForCCallArgument<T>(); }
  
  template<typename T, typename... Ts>
  static constexpr std::enable_if_t<!!sizeof...(Ts), unsigned> computeCCallSlots() { return computeCCallSlots<Ts...>() + slotsForCCallArgument<T>(); }
  
  #endif
  
  template<typename Result, typename... Args>
  struct FunctionTraits<Result(Args...)> {
      using ResultType = Result;
  
      static constexpr bool hasResult = !std::is_same<ResultType, void>::value;
  
      static constexpr std::size_t arity = sizeof...(Args);
  
      template <std::size_t n, typename = std::enable_if_t<(n < arity)>>
      using ArgumentType = typename std::tuple_element<n, std::tuple<Args...>>::type;
      using ArgumentTypes = std::tuple<Args...>;
  
  
  #if USE(JSVALUE64)
      static constexpr unsigned cCallArity() { return arity; }
  #else
  
      static constexpr unsigned cCallArity() { return computeCCallSlots<Args...>(); }
  #endif // USE(JSVALUE64)
  
  };
  
  template<typename Result, typename... Args>
  struct FunctionTraits<Result(*)(Args...)> : public FunctionTraits<Result(Args...)> {
  };
  
  } // namespace WTF
  
  using WTF::FunctionTraits;
  