72 lines
1.8 KiB
C
72 lines
1.8 KiB
C
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/*
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* This file is part of the DXX-Rebirth project <http://www.dxx-rebirth.com/>.
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* It is copyright by its individual contributors, as recorded in the
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* project's Git history. See COPYING.txt at the top level for license
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* terms and a link to the Git history.
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*/
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#pragma once
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#include <iterator>
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#include <utility>
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template <typename T>
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class self_return_iterator :
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public std::iterator<std::forward_iterator_tag, T>,
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T
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{
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public:
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self_return_iterator(T &&i) :
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T(std::move(i))
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{
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}
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T base() const
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{
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return *this;
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}
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T operator*() const
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{
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return *this;
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}
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/* Some STL algorithms require:
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*
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* !!std::is_same<decltype(iter), decltype(++iter)>::value
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*
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* If this requirement is not met, template argument deduction
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* fails when the algorithm calls a helper function.
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*
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* If not for this requirement, `using T::operator++` would have
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* been sufficient here.
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*/
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self_return_iterator &operator++()
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{
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/* Use a static_cast instead of ignoring the return value and
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* returning `*this`, to encourage the compiler to implement
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* this as a tail-call when
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*
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* offsetof(self_return_iterator, T) == 0
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*/
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return static_cast<self_return_iterator &>(this->T::operator++());
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}
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/* operator++(int) is currently unused, but is required to satisfy
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* the concept check on forward iterator.
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*/
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self_return_iterator operator++(int)
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{
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auto result = *this;
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this->T::operator++();
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return result;
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}
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/* Since `T` is inherited privately, the base class `operator==` and
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* `operator!=` cannot implicitly convert `rhs` to `T`. Define
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* comparison operators to perform the conversion explicitly.
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*/
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bool operator==(const self_return_iterator &rhs) const
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{
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return this->T::operator==(static_cast<const T &>(rhs));
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}
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bool operator!=(const self_return_iterator &rhs) const
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{
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return this->T::operator!=(static_cast<const T &>(rhs));
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}
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};
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