type_traits.h

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//===- llvm/Support/type_traits.h - Simplfied type traits -------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file provides useful additions to the standard type_traits library.
//
//===----------------------------------------------------------------------===//
 
#ifndef WPIUTIL_WPI_TYPE_TRAITS_H
#define WPIUTIL_WPI_TYPE_TRAITS_H
 
#include "wpi/Compiler.h"
#include <type_traits>
#include <utility>
 
namespace wpi {
 
 
/// Metafunction that determines whether the given type is either an
/// integral type or an enumeration type, including enum classes.
///
/// Note that this accepts potentially more integral types than is_integral
/// because it is based on being implicitly convertible to an integral type.
/// Also note that enum classes aren't implicitly convertible to integral types,
/// the value may therefore need to be explicitly converted before being used.
template <typename T> class is_integral_or_enum {
  using UnderlyingT = std::remove_reference_t<T>;
 
public:
  static const bool value =
      !std::is_class_v<UnderlyingT> && // Filter conversion operators.
      !std::is_pointer_v<UnderlyingT> &&
      !std::is_floating_point_v<UnderlyingT> &&
      (std::is_enum_v<UnderlyingT> ||
       std::is_convertible_v<UnderlyingT, unsigned long long>);
};
 
/// If T is a pointer, just return it. If it is not, return T&.
template<typename T, typename Enable = void>
struct add_lvalue_reference_if_not_pointer { using type = T &; };
 
template <typename T>
struct add_lvalue_reference_if_not_pointer<
    T, std::enable_if_t<std::is_pointer_v<T>>> {
  using type = T;
};
 
/// If T is a pointer to X, return a pointer to const X. If it is not,
/// return const T.
template<typename T, typename Enable = void>
struct add_const_past_pointer { using type = const T; };
 
template <typename T>
struct add_const_past_pointer<T, std::enable_if_t<std::is_pointer_v<T>>> {
  using type = const std::remove_pointer_t<T> *;
};
 
template <typename T, typename Enable = void>
struct const_pointer_or_const_ref {
  using type = const T &;
};
template <typename T>
struct const_pointer_or_const_ref<T, std::enable_if_t<std::is_pointer_v<T>>> {
  using type = typename add_const_past_pointer<T>::type;
};
 
namespace detail {
template<class T>
union trivial_helper {
    T t;
};
 
} // end namespace detail
 
// https://stackoverflow.com/questions/55288555/c-check-if-statement-can-be-evaluated-constexpr
template<class Lambda, int=(Lambda{}(), 0)>
constexpr bool is_constexpr(Lambda) { return true; }
constexpr bool is_constexpr(...) { return false; }
 
} // end namespace wpi
 
#endif // WPIUTIL_WPI_TYPE_TRAITS_H