swoc_meta.h

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// SPDX-License-Identifier: Apache-2.0
// Copyright Verizon Media 2020
 
#pragma once
 
#include <type_traits>
#include <utility>
 
#include "swoc/swoc_version.h"
 
namespace swoc { inline namespace SWOC_VERSION_NS { namespace meta {

template <unsigned N> struct CaseTag :  public CaseTag<N - 1>  {
  constexpr CaseTag() {}
 
  static constexpr unsigned value = N; 
};

template <> struct CaseTag<0> {
  constexpr CaseTag() {}
 
  static constexpr unsigned value = 0; 
};

static constexpr CaseTag<9> CaseArg{};

template <typename T> T TypeFunc();

template <typename T, typename U>
constexpr auto
eraser(U &&u) -> U {
  return std::forward<U>(u);
}

template <typename... Args> struct vary : public Args... {
  using Args::operator()...;
};

template <typename... Args> vary(Args...) -> vary<Args...>;

template <typename T, typename... Types> struct is_any_of {
  static constexpr bool value = std::disjunction<std::is_same<T, Types>...>::value;
};
 
template <typename T, typename... Types> struct is_homogenous {
  static constexpr bool value = std::conjunction<std::is_same<T, Types>...>::value;
  using type                  = T;
};

template <typename T, typename... Types> inline constexpr bool is_any_of_v = is_any_of<T, Types...>::value;

template <typename... Types> struct type_list {
  static constexpr size_t size = sizeof...(Types);

  template <template <typename... Pack> typename T> using apply = T<Types...>;

  template <typename T> static constexpr bool contains = is_any_of<T, Types...>::value;
};

template <typename T> struct let {
  using self_type = let;
 
  let(self_type const &that)              = delete;
  self_type &operator=(self_type const &) = delete;
 
  T &_var;  
  T _value; 

  let(T &var, T const &value);

  let(T &var, T &&value);
 
  ~let();
};
 
template <typename T> let<T>::let(T &var, T const &value) : _var(var), _value(std::move(var)) {
  _var = value;
}
template <typename T> let<T>::let(T &var, T &&value) : _var(var), _value(std::move(var)) {
  _var = std::move(value);
}
 
template <typename T> let<T>::~let() {
  _var = std::move(_value);
}
 
}}} // namespace swoc::SWOC_VERSION_NS::meta