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// Copyright 2018 Google LLC
//
// 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 ASTC_CODEC_BASE_TYPE_TRAITS_H_
#define ASTC_CODEC_BASE_TYPE_TRAITS_H_
#include <iterator>
#include <type_traits>
namespace astc_codec {
namespace base {
namespace details {
// a simple helper class for SFINAE below.
template<class X = void>
struct dummy {
using type = X;
};
} // namespace details
// add some convenience shortcuts for an overly complex std::enable_if syntax
// Use 'enable_if<Predicate,Type>' instead of
// 'typename std::enable_if<Predicate::value,Type>::type'
template<class Predicate, class Type = void*>
using enable_if = typename std::enable_if<Predicate::value, Type>::type;
// Use 'enable_if_c<BooleanFlag,Type>' instead of
// 'typename std::enable_if<BooleanFlag,Type>::type'
template<bool predicate, class Type = void*>
using enable_if_c = typename std::enable_if<predicate, Type>::type;
// Use 'enable_if_convertible<From,To,Type>' instead of
// 'typename std::enable_if<std::is_convertible<From,To>::value, Type>::type'
template<class From, class To, class Type = void*>
using enable_if_convertible = enable_if<std::is_convertible<From, To>>;
// -----------------------------------------------------------------------------
// A predicate for checking if some object is callable with a specific
// signature. Examples:
//
// is_callable_as<int, void()>::value == false.
// is_callable_as<strcmp, void()>::value == false.
// is_callable_as<strcmp, int(const char*, const char*)>::value == true
//
template<class F, class Signature, class X = void>
struct is_callable_as : std::false_type {};
// This specialization is SFINAE-d out if template arguments can't be combined
// into a call expression F(), or if the result of that call is not |R|
template<class F, class R, class... Args>
struct is_callable_as<F, R(Args...),
typename std::enable_if<std::is_same<
typename details::dummy<decltype(std::declval<F>()(
std::declval<Args>()...))>::type,
R>::value>::type> : std::true_type {};
//
// A similar predicate to only check arguments of the function call and ignore
// the specified return type
//
// is_callable_as<strcmp, int(const char*, const char*)>::value == true
// is_callable_as<strcmp, void(const char*, const char*)>::value == false
// is_callable_with_args<strcmp, void(const char*, const char*)>::value == true
//
template<class F, class Signature, class X = void>
struct is_callable_with_args : std::false_type {};
template<class F, class R, class... Args>
struct is_callable_with_args<
F, R(Args...),
typename std::enable_if<
!std::is_same<typename details::dummy<decltype(
std::declval<F>()(std::declval<Args>()...))>::type,
F>::value>::type> : std::true_type {};
// -----------------------------------------------------------------------------
// Check if a type |T| is any instantiation of a template |U|. Examples:
//
// is_template_instantiation_of<int, std::vector>::value == false
// is_template_instantiation_of<
// std::list<std::vector<int>>, std::vector>::value == false
// is_template_instantiation_of<std::vector<int>, std::vector>::value == true
// is_template_instantiation_of<
// std::vector<std::vector<int>>, std::vector>::value == true
//
template<class T, template<class...> class U>
struct is_template_instantiation_of : std::false_type {};
template<template<class...> class U, class... Args>
struct is_template_instantiation_of<U<Args...>, U> : std::true_type {};
// -----------------------------------------------------------------------------
//
// is_range<T> - check if type |T| is a range-like type.
//
// It makes sure that expressions std::begin(t) and std::end(t) are well-formed
// and those return the same type.
//
// Note: with expression SFINAE from C++14 is_range_helper<> could be renamed to
// is_range<> with no extra code. C++11 needs an extra level of enable_if<>
// to make it work when the type isn't a range.
//
namespace details {
template<class T>
using is_range_helper = std::is_same<
decltype(std::begin(
std::declval<typename std::add_lvalue_reference<T>::type>())),
decltype(
std::end(std::declval<typename std::add_lvalue_reference<T>::type>()))>;
} // namespace details
template<class T, class = void>
struct is_range : std::false_type {};
template<class T>
struct is_range<
T, typename std::enable_if<details::is_range_helper<T>::value>::type>
: std::true_type {};
////////////////////////////////////////////////////////////////////////////////
//
// A class to incapsulate integer sequence 0, 1, ..., <num_args>
// Seq<int...>
// Useful to pass function parameters in an array/tuple to call it later.
//
template<int...>
struct Seq {};
// A 'maker' class to construct Seq<int...> given only <num_args>
// value.
// MakeSeq<N, S...> works this way, e.g.
//
// MakeSeq<2> inherits MakeSeq<2 - 1, 2 - 1> == MakeSeq<1, 1>
// MakeSeq<1, 1> : MakeSeq<1 - 1, 1 - 1, 1> == MakeSeq<0, 0, 1>
// MakeSeq<0, 0, 1> == MakeSeq<0, S...> and defines |type| = Seq<0, 1>
template<int N, int... S>
struct MakeSeq : MakeSeq<N - 1, N - 1, S...> {};
template<int... S>
struct MakeSeq<0, S...> {
using type = Seq<S...>;
};
//
// MakeSeqT alias to quickly create Seq<...>:
// MakeSeqT<3> == Seq<0, 1, 2>
template<int... S>
using MakeSeqT = typename MakeSeq<S...>::type;
} // namespace base
} // namespace astc_codec
#endif // ASTC_CODEC_BASE_TYPE_TRAITS_H_
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