sfinae_helpers.h

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// Copyright (c) 2016-2018, The Monero Project
// 
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// 
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// 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.
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//    used to endorse or promote products derived from this software without specific
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// 
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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