absl/random/internal/distributions.h

// Copyright 2019 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef ABSL_RANDOM_INTERNAL_DISTRIBUTIONS_H_
#define ABSL_RANDOM_INTERNAL_DISTRIBUTIONS_H_

#include <type_traits>

#include "absl/meta/type_traits.h"
#include "absl/random/internal/distribution_caller.h"
#include "absl/random/internal/traits.h"
#include "absl/random/internal/uniform_helper.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {

// In the absence of an explicitly provided return-type, the template
// "uniform_inferred_return_t<A, B>" is used to derive a suitable type, based on
// the data-types of the endpoint-arguments {A lo, B hi}.
//
// Given endpoints {A lo, B hi}, one of {A, B} will be chosen as the
// return-type, if one type can be implicitly converted into the other, in a
// lossless way. The template "is_widening_convertible" implements the
// compile-time logic for deciding if such a conversion is possible.
//
// If no such conversion between {A, B} exists, then the overload for
// absl::Uniform() will be discarded, and the call will be ill-formed.
// Return-type for absl::Uniform() when the return-type is inferred.
template <typename A, typename B>
using uniform_inferred_return_t =
    absl::enable_if_t<absl::disjunction<is_widening_convertible<A, B>,
                                        is_widening_convertible<B, A>>::value,
                      typename std::conditional<
                          is_widening_convertible<A, B>::value, B, A>::type>;

}  // namespace random_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_RANDOM_INTERNAL_DISTRIBUTIONS_H_