From Jason Turner

[range.utility.conv]

C++23 → Trunk 3.2 KB 41 lines
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Archived: C++23
Markdown: C++23 | Trunk
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  1. tmp/tmpp5iw6hxb/{from.md → to.md} +23 -14
tmp/tmpp5iw6hxb/{from.md → to.md} RENAMED
@@ -31,30 +31,38 @@ constexpr bool reservable-container = // exposition only
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  { c.capacity() } -> same_as<decltype(n)>;
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  { c.max_size() } -> same_as<decltype(n)>;
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  };
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  ```
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- Let *`container-insertable`* be defined as follows:
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  ``` cpp
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  template<class Container, class Ref>
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- constexpr bool container-insertable = // exposition only
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  requires(Container& c, Ref&& ref) {
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- requires (requires { c.push_back(std::forward<Ref>(ref)); } ||
 
 
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  requires { c.insert(c.end(), std::forward<Ref>(ref)); });
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  };
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  ```
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- Let *`container-inserter`* be defined as follows:
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  ``` cpp
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- template<class Ref, class Container>
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- constexpr auto container-inserter(Container& c) { // exposition only
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- if constexpr (requires { c.push_back(declval<Ref>()); })
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- return back_inserter(c);
 
 
 
 
 
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  else
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- return inserter(c, c.end());
 
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  }
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  ```
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  #### `ranges::to` <a id="range.utility.conv.to">[[range.utility.conv.to]]</a>
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@@ -90,21 +98,22 @@ the following manner:
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  ``` cpp
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  C(ranges::begin(r), ranges::end(r), std::forward<Args>(args)...)
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  ```
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  - Otherwise, if
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  - `constructible_from<C, Args...>` is `true`, and
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- - *`container-insertable`*`<C, range_reference_t<R>>` is `true`:
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  ``` cpp
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  C c(std::forward<Args>(args)...);
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- if constexpr (sized_range<R> && reservable-container<C>)
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- c.reserve(static_cast<range_size_t<C>>(ranges::size(r)));
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- ranges::copy(r, container-inserter<range_reference_t<R>>(c));
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  ```
 
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  - Otherwise, if `input_range<range_reference_t<R>>` is `true`:
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  ``` cpp
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- to<C>(r | views::transform([](auto&& elem) {
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  return to<range_value_t<C>>(std::forward<decltype(elem)>(elem));
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  }), std::forward<Args>(args)...);
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  ```
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  - Otherwise, the program is ill-formed.
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  { c.capacity() } -> same_as<decltype(n)>;
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  { c.max_size() } -> same_as<decltype(n)>;
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  };
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  ```
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+ Let *`container-appendable`* be defined as follows:
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  ``` cpp
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  template<class Container, class Ref>
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+ constexpr bool container-appendable = // exposition only
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  requires(Container& c, Ref&& ref) {
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+ requires (requires { c.emplace_back(std::forward<Ref>(ref)); } ||
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+ requires { c.push_back(std::forward<Ref>(ref)); } ||
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+ requires { c.emplace(c.end(), std::forward<Ref>(ref)); } ||
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  requires { c.insert(c.end(), std::forward<Ref>(ref)); });
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  };
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  ```
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+ Let *`container-append`* be defined as follows:
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  ``` cpp
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+ template<class Container>
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+ constexpr auto container-append(Container& c) { // exposition only
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+ return [&c]<class Ref>(Ref&& ref) {
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+ if constexpr (requires { c.emplace_back(declval<Ref>()); })
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+ c.emplace_back(std::forward<Ref>(ref));
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+ else if constexpr (requires { c.push_back(declval<Ref>()); })
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+ c.push_back(std::forward<Ref>(ref));
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+ else if constexpr (requires { c.emplace(c.end(), declval<Ref>()); })
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+ c.emplace(c.end(), std::forward<Ref>(ref));
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  else
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+ c.insert(c.end(), std::forward<Ref>(ref));
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+ };
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  }
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  ```
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  #### `ranges::to` <a id="range.utility.conv.to">[[range.utility.conv.to]]</a>
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  ``` cpp
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  C(ranges::begin(r), ranges::end(r), std::forward<Args>(args)...)
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  ```
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  - Otherwise, if
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  - `constructible_from<C, Args...>` is `true`, and
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+ - *`container-appendable`*`<C, range_reference_t<R>>` is `true`:
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  ``` cpp
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  C c(std::forward<Args>(args)...);
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+ if constexpr (approximately_sized_range<R> && reservable-container<C>)
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+ c.reserve(static_cast<range_size_t<C>>(ranges::reserve_hint(r)));
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+ ranges::for_each(r, container-append(c));
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  ```
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+ - Otherwise, the program is ill-formed.
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  - Otherwise, if `input_range<range_reference_t<R>>` is `true`:
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  ``` cpp
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+ to<C>(ref_view(r) | views::transform([](auto&& elem) {
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  return to<range_value_t<C>>(std::forward<decltype(elem)>(elem));
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  }), std::forward<Args>(args)...);
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  ```
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  - Otherwise, the program is ill-formed.
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