tmp/tmp0rwasny0/{from.md → to.md}
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### Dangling iterator handling <a id="range.dangling">[[range.dangling]]</a>
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The tag type `dangling` is used together with the template aliases
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`borrowed_iterator_t` and `borrowed_subrange_t` to indicate that an
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algorithm that typically returns an iterator into or subrange of a
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`range` argument does not return an iterator or subrange which could
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potentially reference a range whose lifetime has ended for a particular
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rvalue `range` argument which does not model `borrowed_range`
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[[range.range]].
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``` cpp
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namespace std::ranges {
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struct dangling {
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constexpr dangling() noexcept = default;
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template<class... Args>
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constexpr dangling(Args&&...) noexcept { }
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};
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}
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```
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[*Example 1*:
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``` cpp
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vector<int> f();
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auto result1 = ranges::find(f(), 42); // #1
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static_assert(same_as<decltype(result1), ranges::dangling>);
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auto vec = f();
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auto result2 = ranges::find(vec, 42); // #2
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static_assert(same_as<decltype(result2), vector<int>::iterator>);
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auto result3 = ranges::find(subrange{vec}, 42); // #3
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static_assert(same_as<decltype(result3), vector<int>::iterator>);
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```
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The call to `ranges::find` at \#1 returns `ranges::dangling` since `f()`
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is an rvalue `vector`; the `vector` could potentially be destroyed
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before a returned iterator is dereferenced. However, the calls at \#2
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and \#3 both return iterators since the lvalue `vec` and specializations
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of `subrange` model `borrowed_range`.
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— *end example*]
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