tmp/tmp7s4lwlxm/{from.md → to.md}
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| 1 |
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#### Overview <a id="range.elements.overview">[[range.elements.overview]]</a>
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`elements_view` takes a `view` of tuple-like values and a `size_t`, and
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produces a `view` with a value-type of the Nᵗʰ element of the adapted
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`view`’s value-type.
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The name `views::elements<N>` denotes a range adaptor object
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[[range.adaptor.object]]. Given a subexpression `E` and constant
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expression `N`, the expression `views::elements<N>(E)` is
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expression-equivalent to
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`elements_view<views::all_t<decltype((E))>, N>{E}`.
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[*Example 1*:
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``` cpp
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auto historical_figures = map{
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{"Lovelace"sv, 1815},
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{"Turing"sv, 1912},
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{"Babbage"sv, 1791},
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{"Hamilton"sv, 1936}
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};
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auto names = historical_figures | views::elements<0>;
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for (auto&& name : names) {
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cout << name << ' '; // prints Babbage Hamilton Lovelace Turing
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}
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auto birth_years = historical_figures | views::elements<1>;
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for (auto&& born : birth_years) {
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cout << born << ' '; // prints 1791 1936 1815 1912
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}
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```
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— *end example*]
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`keys_view` is an alias for `elements_view<views::all_t<R>, 0>`, and is
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useful for extracting keys from associative containers.
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[*Example 2*:
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``` cpp
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auto names = keys_view{historical_figures};
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for (auto&& name : names) {
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cout << name << ' '; // prints Babbage Hamilton Lovelace Turing
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}
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```
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— *end example*]
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`values_view` is an alias for `elements_view<views::all_t<R>, 1>`, and
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is useful for extracting values from associative containers.
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[*Example 3*:
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``` cpp
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auto is_even = [](const auto x) { return x % 2 == 0; };
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cout << ranges::count_if(values_view{historical_figures}, is_even); // prints 2
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```
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— *end example*]
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