From Jason Turner

[range.range]

C++20 → C++23 2.6 KB 29 lines
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Archived: C++20 | C++23
Markdown: C++20 | C++23
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  1. tmp/tmp6jqgtbq2/{from.md → to.md} +13 -13
tmp/tmp6jqgtbq2/{from.md → to.md} RENAMED
@@ -26,37 +26,37 @@ Given an expression `t` such that `decltype((t))` is `T&`, `T` models
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  time and non-modifying, and
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  - if the type of `ranges::begin(t)` models `forward_iterator`,
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  `ranges::begin(t)` is equality-preserving.
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  [*Note 1*: Equality preservation of both `ranges::begin` and
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- `ranges::end` enables passing a `range` whose iterator type models
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  `forward_iterator` to multiple algorithms and making multiple passes
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  over the range by repeated calls to `ranges::begin` and `ranges::end`.
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  Since `ranges::begin` is not required to be equality-preserving when the
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- return type does not model `forward_iterator`, repeated calls might not
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- return equal values or might not be well-defined; `ranges::begin` should
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- be called at most once for such a range. — *end note*]
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  ``` cpp
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  template<class T>
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  concept borrowed_range =
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- range<T> &&
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- (is_lvalue_reference_v<T> || enable_borrowed_range<remove_cvref_t<T>>);
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  ```
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- Given an expression `E` such that `decltype((E))` is `T`, `T` models
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- `borrowed_range` only if the validity of iterators obtained from the
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- object denoted by `E` is not tied to the lifetime of that object.
 
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  [*Note 2*: Since the validity of iterators is not tied to the lifetime
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- of an object whose type models `borrowed_range`, a function can accept
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- arguments of such a type by value and return iterators obtained from it
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- without danger of dangling. — *end note*]
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  ``` cpp
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  template<class>
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- inline constexpr bool enable_borrowed_range = false;
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  ```
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  *Remarks:* Pursuant to [[namespace.std]], users may specialize
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  `enable_borrowed_range` for cv-unqualified program-defined types. Such
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  specializations shall be usable in constant expressions [[expr.const]]
 
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  time and non-modifying, and
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  - if the type of `ranges::begin(t)` models `forward_iterator`,
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  `ranges::begin(t)` is equality-preserving.
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  [*Note 1*: Equality preservation of both `ranges::begin` and
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+ `ranges::end` enables passing a range whose iterator type models
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  `forward_iterator` to multiple algorithms and making multiple passes
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  over the range by repeated calls to `ranges::begin` and `ranges::end`.
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  Since `ranges::begin` is not required to be equality-preserving when the
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+ return type does not model `forward_iterator`, it is possible for
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+ repeated calls to not return equal values or to not be
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+ well-defined. — *end note*]
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  ``` cpp
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  template<class T>
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  concept borrowed_range =
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+ range<T> && (is_lvalue_reference_v<T> || enable_borrowed_range<remove_cvref_t<T>>);
 
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  ```
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+ Let `U` be `remove_reference_t<T>` if `T` is an rvalue reference type,
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+ and `T` otherwise. Given a variable `u` of type `U`, `T` models
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+ `borrowed_range` only if the validity of iterators obtained from `u` is
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+ not tied to the lifetime of that variable.
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  [*Note 2*: Since the validity of iterators is not tied to the lifetime
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+ of a variable whose type models `borrowed_range`, a function with a
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+ parameter of such a type can return iterators obtained from it without
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+ danger of dangling. — *end note*]
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  ``` cpp
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  template<class>
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+ constexpr bool enable_borrowed_range = false;
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  ```
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  *Remarks:* Pursuant to [[namespace.std]], users may specialize
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  `enable_borrowed_range` for cv-unqualified program-defined types. Such
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  specializations shall be usable in constant expressions [[expr.const]]