tmp/tmp8kw79g1n/{from.md → to.md}
RENAMED
|
@@ -0,0 +1,39 @@
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| 1 |
+
### Concept <a id="concept.convertible">[[concept.convertible]]</a>
|
| 2 |
+
|
| 3 |
+
Given types `From` and `To` and an expression `E` such that
|
| 4 |
+
`decltype((E))` is `add_rvalue_reference_t<From>`,
|
| 5 |
+
`convertible_to<From, To>` requires `E` to be both implicitly and
|
| 6 |
+
explicitly convertible to type `To`. The implicit and explicit
|
| 7 |
+
conversions are required to produce equal results.
|
| 8 |
+
|
| 9 |
+
``` cpp
|
| 10 |
+
template<class From, class To>
|
| 11 |
+
concept convertible_to =
|
| 12 |
+
is_convertible_v<From, To> &&
|
| 13 |
+
requires(add_rvalue_reference_t<From> (&f)()) {
|
| 14 |
+
static_cast<To>(f());
|
| 15 |
+
};
|
| 16 |
+
```
|
| 17 |
+
|
| 18 |
+
Let `FromR` be `add_rvalue_reference_t<From>` and `test` be the invented
|
| 19 |
+
function:
|
| 20 |
+
|
| 21 |
+
``` cpp
|
| 22 |
+
To test(FromR (&f)()) {
|
| 23 |
+
return f();
|
| 24 |
+
}
|
| 25 |
+
```
|
| 26 |
+
|
| 27 |
+
and let `f` be a function with no arguments and return type `FromR` such
|
| 28 |
+
that `f()` is equality-preserving. Types `From` and `To` model
|
| 29 |
+
`convertible_to<From, To>` only if:
|
| 30 |
+
|
| 31 |
+
- `To` is not an object or reference-to-object type, or
|
| 32 |
+
`static_cast<To>(f())` is equal to `test(f)`.
|
| 33 |
+
- `FromR` is not a reference-to-object type, or
|
| 34 |
+
- If `FromR` is an rvalue reference to a non const-qualified type, the
|
| 35 |
+
resulting state of the object referenced by `f()` after either above
|
| 36 |
+
expression is valid but unspecified [[lib.types.movedfrom]].
|
| 37 |
+
- Otherwise, the object referred to by `f()` is not modified by either
|
| 38 |
+
above expression.
|
| 39 |
+
|