concepts.h

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// This file's extension implies that it's C, but it's really -*- C++ -*-.
/*
 * Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration.
 */
#ifndef CXXUTILS_CONCEPTS_H
#define CXXUTILS_CONCEPTS_H
 
 
#include <type_traits>
#include <iterator>
 
 
#ifdef __cpp_concepts
 
#define HAVE_CONCEPTS 1
 
#include <concepts>
#define ATH_REQUIRES(...) requires __VA_ARGS__
 
#define ATH_MEMBER_REQUIRES(CONDITION, RETTYPE) \
  template <bool = true> \
  requires (CONDITION)   \
  RETTYPE
 
#define ATH_MEMBER_REQUIRES_DEF(CONDITION, RETTYPE) \
  template <bool> \
  requires (CONDITION)   \
  RETTYPE
 
 
// Some library concepts.
 
namespace CxxUtils {
namespace detail {
 
 
// Standard library Hash requirement.
template <class HASHER, class T>
concept IsHash =
  std::destructible<HASHER> &&
  std::copy_constructible<HASHER> &&
  requires (const HASHER& h, T x)
{
  { h(x) } -> std::same_as<std::size_t>;
};
 
 
// Standard library BinaryPredicate requirement.
template <class PRED, class ARG1, class ARG2=ARG1>
concept IsBinaryPredicate =
  std::copy_constructible<PRED> &&
  std::predicate<PRED, ARG1, ARG2>;
 
 
template <class CONTAINER>
concept IsContiguousContainer =
  requires (CONTAINER& c)
  {
    requires std::contiguous_iterator<decltype(c.begin())>;
  };
 
 
template <class ITERATOR, class VAL>
concept InputValIterator =
  std::input_iterator<ITERATOR> &&
  std::convertible_to<std::iter_value_t<ITERATOR>, VAL>;
 
 
} // namespace detail
} // namespace CxxUtils
 
#else
 
#define HAVE_CONCEPTS 0
 
#define ATH_REQUIRES(...)
 
#define ATH_MEMBER_REQUIRES(CONDITION, RETTYPE) \
  template <bool Enable = true> \
  std::enable_if_t<Enable && (CONDITION), RETTYPE>
 
#define ATH_MEMBER_REQUIRES_DEF(CONDITION, RETTYPE) \
  template <bool Enable> \
  std::enable_if_t<Enable && (CONDITION), RETTYPE>
 
#endif
 
 
#endif // not CXXUTILS_CONCEPTS_H