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/*
* Copyright (C) 2016 The Android Open Source Project
*
* 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
*
* http://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 ART_LIBARTBASE_BASE_TRANSFORM_ITERATOR_H_
#define ART_LIBARTBASE_BASE_TRANSFORM_ITERATOR_H_
#include <iterator>
#include <type_traits>
#include "iteration_range.h"
namespace art {
// The transform iterator transforms values from the base iterator with a given
// transformation function. It can serve as a replacement for std::transform(), i.e.
// std::copy(MakeTransformIterator(begin, f), MakeTransformIterator(end, f), out)
// is equivalent to
// std::transform(begin, end, f)
// If the function returns an l-value reference or a wrapper that supports assignment,
// the TransformIterator can be used also as an output iterator, i.e.
// std::copy(begin, end, MakeTransformIterator(out, f))
// is equivalent to
// for (auto it = begin; it != end; ++it) {
// f(*out++) = *it;
// }
template <typename BaseIterator, typename Function>
class TransformIterator {
private:
static_assert(std::is_base_of<
std::input_iterator_tag,
typename std::iterator_traits<BaseIterator>::iterator_category>::value,
"Transform iterator base must be an input iterator.");
using InputType = typename std::iterator_traits<BaseIterator>::reference;
using ResultType = typename std::result_of<Function(InputType)>::type;
public:
using iterator_category = typename std::iterator_traits<BaseIterator>::iterator_category;
using value_type =
typename std::remove_const<typename std::remove_reference<ResultType>::type>::type;
using difference_type = typename std::iterator_traits<BaseIterator>::difference_type;
using pointer = typename std::conditional<
std::is_reference<ResultType>::value,
typename std::add_pointer<typename std::remove_reference<ResultType>::type>::type,
TransformIterator>::type;
using reference = ResultType;
TransformIterator(BaseIterator base, Function fn)
: data_(base, fn) { }
template <typename OtherBI>
TransformIterator(const TransformIterator<OtherBI, Function>& other)
: data_(other.base(), other.GetFunction()) {
}
TransformIterator& operator++() {
++data_.base_;
return *this;
}
TransformIterator operator++(int) {
TransformIterator tmp(*this);
++*this;
return tmp;
}
TransformIterator& operator--() {
static_assert(
std::is_base_of<std::bidirectional_iterator_tag,
typename std::iterator_traits<BaseIterator>::iterator_category>::value,
"BaseIterator must be bidirectional iterator to use operator--()");
--data_.base_;
return *this;
}
TransformIterator operator--(int) {
TransformIterator tmp(*this);
--*this;
return tmp;
}
reference operator*() const {
return GetFunction()(*base());
}
reference operator[](difference_type n) const {
static_assert(
std::is_base_of<std::random_access_iterator_tag,
typename std::iterator_traits<BaseIterator>::iterator_category>::value,
"BaseIterator must be random access iterator to use operator[]");
return GetFunction()(base()[n]);
}
TransformIterator operator+(difference_type n) const {
static_assert(
std::is_base_of<std::random_access_iterator_tag,
typename std::iterator_traits<BaseIterator>::iterator_category>::value,
"BaseIterator must be random access iterator to use operator+");
return TransformIterator(base() + n, GetFunction());
}
TransformIterator operator-(difference_type n) const {
static_assert(
std::is_base_of<std::random_access_iterator_tag,
typename std::iterator_traits<BaseIterator>::iterator_category>::value,
"BaseIterator must be random access iterator to use operator-");
return TransformIterator(base() - n, GetFunction());
}
difference_type operator-(const TransformIterator& other) const {
static_assert(
std::is_base_of<std::random_access_iterator_tag,
typename std::iterator_traits<BaseIterator>::iterator_category>::value,
"BaseIterator must be random access iterator to use operator-");
return base() - other.base();
}
// Retrieve the base iterator.
BaseIterator base() const {
return data_.base_;
}
// Retrieve the transformation function.
const Function& GetFunction() const {
return static_cast<const Function&>(data_);
}
private:
// Allow EBO for state-less Function.
struct Data : Function {
public:
Data(BaseIterator base, Function fn) : Function(fn), base_(base) { }
BaseIterator base_;
};
Data data_;
};
template <typename BaseIterator1, typename BaseIterator2, typename Function>
bool operator==(const TransformIterator<BaseIterator1, Function>& lhs,
const TransformIterator<BaseIterator2, Function>& rhs) {
return lhs.base() == rhs.base();
}
template <typename BaseIterator1, typename BaseIterator2, typename Function>
bool operator!=(const TransformIterator<BaseIterator1, Function>& lhs,
const TransformIterator<BaseIterator2, Function>& rhs) {
return !(lhs == rhs);
}
template <typename BaseIterator, typename Function>
TransformIterator<BaseIterator, Function> MakeTransformIterator(BaseIterator base, Function f) {
return TransformIterator<BaseIterator, Function>(base, f);
}
template <typename BaseRange, typename Function>
auto MakeTransformRange(BaseRange& range, Function f) {
return MakeIterationRange(MakeTransformIterator(range.begin(), f),
MakeTransformIterator(range.end(), f));
}
} // namespace art
#endif // ART_LIBARTBASE_BASE_TRANSFORM_ITERATOR_H_
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