sfinae_helpers.h

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// Copyright (c) 2016-2022, The Monero Project
// 
// 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.
// 
// 3. Neither the name of the copyright holder nor the names of its contributors may be
//    used to endorse or promote products derived from this software without specific
//    prior written permission.
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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#pragma once
 
// the loose definitions of types in this file are, well, loose.
//
// these helpers aren't here for absolute type certainty at compile-time,
// but rather to help with templated functions telling types apart.
 
namespace sfinae
{
 
  typedef char true_type;
 
  struct false_type { true_type a[2]; };
 
  template <typename T>
  struct is_not_container
  {
  private:
 
    // does not have const iterator
    template <typename C> static false_type c_iter(typename C::const_iterator*);
    template <typename C> static true_type c_iter(...);
 
    // does not have value_type
    template <typename C> static false_type v_type(typename C::value_type*);
    template <typename C> static true_type v_type(...);
 
    // does not have key_type
    template <typename C> static false_type k_type(typename C::key_type*);
    template <typename C> static true_type k_type(...);
 
    // does not have mapped_type
    template <typename C> static false_type m_type(typename C::mapped_type*);
    template <typename C> static true_type m_type(...);
 
  public:
 
    static const bool value = (
      (
        sizeof(c_iter<T>(0)) == sizeof(true_type) &&
        sizeof(v_type<T>(0)) == sizeof(true_type) &&
        sizeof(k_type<T>(0)) == sizeof(true_type) &&
        sizeof(m_type<T>(0)) == sizeof(true_type)
      )
      || std::is_same<T, std::string>::value
    );
 
    typedef T type;
  };
 
  template <typename T>
  struct is_vector_like
  {
  private:
 
    // has const iterator
    template <typename C> static true_type c_iter(typename C::const_iterator*);
    template <typename C> static false_type c_iter(...);
 
    // has value_type
    template <typename C> static true_type v_type(typename C::value_type*);
    template <typename C> static false_type v_type(...);
 
    // does not have key_type
    template <typename C> static false_type k_type(typename C::key_type*);
    template <typename C> static true_type k_type(...);
 
    // does not have mapped_type
    template <typename C> static false_type m_type(typename C::mapped_type*);
    template <typename C> static true_type m_type(...);
 
  public:
 
    static const bool value = (
        sizeof(c_iter<T>(0)) == sizeof(true_type) &&
        sizeof(v_type<T>(0)) == sizeof(true_type) &&
        sizeof(k_type<T>(0)) == sizeof(true_type) &&
        sizeof(m_type<T>(0)) == sizeof(true_type) &&
        !std::is_same<T, std::string>::value
    );
 
    typedef T type;
  };
 
  template <typename T>
  struct is_map_like
  {
  private:
 
    // has const iterator
    template <typename C> static true_type c_iter(typename C::const_iterator*);
    template <typename C> static false_type c_iter(...);
 
    // has value_type
    template <typename C> static true_type v_type(typename C::value_type*);
    template <typename C> static false_type v_type(...);
 
    // has key_type
    template <typename C> static true_type k_type(typename C::key_type*);
    template <typename C> static false_type k_type(...);
 
    // has mapped_type
    template <typename C> static true_type m_type(typename C::mapped_type*);
    template <typename C> static false_type m_type(...);
 
  public:
 
    static const bool value = (
        sizeof(c_iter<T>(0)) == sizeof(true_type) &&
        sizeof(v_type<T>(0)) == sizeof(true_type) &&
        sizeof(k_type<T>(0)) == sizeof(true_type) &&
        sizeof(m_type<T>(0)) == sizeof(true_type) &&
        !std::is_same<T, std::string>::value
    );
 
    typedef T type;
  };
 
}  // namespace sfinae