template_magic.hpp

//
// Created by lukas on 10.04.18.
//
 
#ifndef TCPSPSUITE_TEMPLATE_MAGIC_HPP
#define TCPSPSUITE_TEMPLATE_MAGIC_HPP
 
#include <type_traits>
 
namespace utilities {
 
/*
 * Allows your classes to optionally contain members, without re-writing the
 * whole class in a partial specialization.
 */
template<class T, bool enabled>
struct OptionalMember {} ;
 
template<class T>
struct OptionalMember<T, false> {
  /* Accept anything inside the constructor */
  template<class ... Ts>
  OptionalMember(Ts ...) {}
};
 
template<class T>
struct OptionalMember<T, true> : public T
{
public:
        using T::T;
};
 
  /*
   * Allows switching of member types based on a constexpr
   * bool expression.
   */
  template<class TrueType, class FalseType, bool b>
  struct ConditionalMember {};
 
  template<class TrueType, class FalseType>
  struct ConditionalMember<TrueType, FalseType, true> : public TrueType
  {
  public:
    using TrueType::TrueType;
  };
 
  template<class TrueType, class FalseType>
  struct ConditionalMember<TrueType, FalseType, false> : public FalseType
  {
  public:
    using FalseType::FalseType;
  };
 
 
/*
 * This is inspired by
 *
 * https://stackoverflow.com/questions/34099597/check-if-a-type-is-passed-in-variadic-template-parameter-pack
 *
 * and should be converted to std::disjunction as soon as C++17 becomes available on reasonable
 * compilers.
 */
template<typename QueryT>
constexpr bool pack_contains() {
        return false;
}
 
// Forward
template<typename QueryT, typename First, typename ...Rest>
constexpr bool pack_contains();
 
template<typename QueryT, bool found, typename ...Rest>
constexpr typename std::enable_if<found, bool>::type pack_contains_forward() {
        return true;
}
 
template<typename QueryT, bool found, typename ...Rest>
constexpr typename std::enable_if<! found, bool>::type pack_contains_forward() {
        return pack_contains<QueryT, Rest...>();
}
 
template<typename QueryT, typename First, typename ...Rest>
constexpr bool pack_contains() {
        return pack_contains_forward<QueryT, std::is_same<QueryT, First>::value, Rest...>();
}
 
/*
 * Merges two parameter Packs
 */
 
 
/*
 * Generic class to contain a template parameter pack
 */
template<class ...> struct pack {};
 
}
 
#endif //TCPSPSUITE_TEMPLATE_MAGIC_HPP