tmp/tmpz59f4zht/{from.md → to.md}
RENAMED
|
@@ -0,0 +1,74 @@
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| 1 |
+
### As const view <a id="range.as.const">[[range.as.const]]</a>
|
| 2 |
+
|
| 3 |
+
#### Overview <a id="range.as.const.overview">[[range.as.const.overview]]</a>
|
| 4 |
+
|
| 5 |
+
`as_const_view` presents a view of an underlying sequence as constant.
|
| 6 |
+
That is, the elements of an `as_const_view` cannot be modified.
|
| 7 |
+
|
| 8 |
+
The name `views::as_const` denotes a range adaptor object
|
| 9 |
+
[[range.adaptor.object]]. Let `E` be an expression, let `T` be
|
| 10 |
+
`decltype((E))`, and let `U` be `remove_cvref_t<T>`. The expression
|
| 11 |
+
`views::as_const(E)` is expression-equivalent to:
|
| 12 |
+
|
| 13 |
+
- If `views::all_t<T>` models `constant_range`, then `views::all(E)`.
|
| 14 |
+
- Otherwise, if `U` denotes `empty_view<X>` for some type `X`, then
|
| 15 |
+
`auto(views::empty<const X>)`.
|
| 16 |
+
- Otherwise, if `U` denotes `span<X, Extent>` for some type `X` and some
|
| 17 |
+
extent `Extent`, then `span<const X, Extent>(E)`.
|
| 18 |
+
- Otherwise, if `U` denotes `ref_view<X>` for some type `X` and
|
| 19 |
+
`const X` models `constant_range`, then
|
| 20 |
+
`ref_view(static_cast<const X&>(E.base()))`.
|
| 21 |
+
- Otherwise, if `E` is an lvalue, `const U` models `constant_range`, and
|
| 22 |
+
`U` does not model `view`, then `ref_view(static_cast<const U&>(E))`.
|
| 23 |
+
- Otherwise, `as_const_view(E)`.
|
| 24 |
+
|
| 25 |
+
[*Example 1*:
|
| 26 |
+
|
| 27 |
+
``` cpp
|
| 28 |
+
template<constant_range R>
|
| 29 |
+
void cant_touch_this(R&&);
|
| 30 |
+
|
| 31 |
+
vector<char> hammer = {'m', 'c'};
|
| 32 |
+
span<char> beat = hammer;
|
| 33 |
+
cant_touch_this(views::as_const(beat)); // will not modify the elements of hammer
|
| 34 |
+
```
|
| 35 |
+
|
| 36 |
+
— *end example*]
|
| 37 |
+
|
| 38 |
+
#### Class template `as_const_view` <a id="range.as.const.view">[[range.as.const.view]]</a>
|
| 39 |
+
|
| 40 |
+
``` cpp
|
| 41 |
+
namespace std::ranges {
|
| 42 |
+
template<view V>
|
| 43 |
+
requires input_range<V>
|
| 44 |
+
class as_const_view : public view_interface<as_const_view<V>> {
|
| 45 |
+
V base_ = V(); // exposition only
|
| 46 |
+
|
| 47 |
+
public:
|
| 48 |
+
as_const_view() requires default_initializable<V> = default;
|
| 49 |
+
constexpr explicit as_const_view(V base);
|
| 50 |
+
|
| 51 |
+
constexpr V base() const & requires copy_constructible<V> { return base_; }
|
| 52 |
+
constexpr V base() && { return std::move(base_); }
|
| 53 |
+
|
| 54 |
+
constexpr auto begin() requires (!simple-view<V>) { return ranges::cbegin(base_); }
|
| 55 |
+
constexpr auto begin() const requires range<const V> { return ranges::cbegin(base_); }
|
| 56 |
+
|
| 57 |
+
constexpr auto end() requires (!simple-view<V>) { return ranges::cend(base_); }
|
| 58 |
+
constexpr auto end() const requires range<const V> { return ranges::cend(base_); }
|
| 59 |
+
|
| 60 |
+
constexpr auto size() requires sized_range<V> { return ranges::size(base_); }
|
| 61 |
+
constexpr auto size() const requires sized_range<const V> { return ranges::size(base_); }
|
| 62 |
+
};
|
| 63 |
+
|
| 64 |
+
template<class R>
|
| 65 |
+
as_const_view(R&&) -> as_const_view<views::all_t<R>>;
|
| 66 |
+
}
|
| 67 |
+
```
|
| 68 |
+
|
| 69 |
+
``` cpp
|
| 70 |
+
constexpr explicit as_const_view(V base);
|
| 71 |
+
```
|
| 72 |
+
|
| 73 |
+
*Effects:* Initializes *base\_* with `std::move(base)`.
|
| 74 |
+
|