Difference between revisions of "cpp/named req/CopyConstructible"
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(Added a note about LWG issue #390.) |
Andreas Krug (Talk | contribs) m (.) |
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Given | Given | ||
| − | * {{c|v}}, an [[cpp/language/value_category#lvalue|lvalue]] expression of type {{tt|T}} or {{c/core|const T}} or an [[cpp/language/value category#rvalue|rvalue]] expression of type {{c/core|const T}} | + | * {{c|v}}, an [[cpp/language/value_category#lvalue|lvalue]] expression of type {{tt|T}} or {{c/core|const T}} or an [[cpp/language/value category#rvalue|rvalue]] expression of type {{c/core|const T}}, |
| − | * {{c|u}}, an arbitrary identifier | + | * {{c|u}}, an arbitrary identifier. |
The following expressions must be valid and have their specified effects: | The following expressions must be valid and have their specified effects: | ||
| Line 18: | Line 18: | ||
!Expression||Post-conditions | !Expression||Post-conditions | ||
|- | |- | ||
| − | | {{c|1=T u = v;}} | + | |{{c|1=T u = v;}} |
| − | | The value of {{c|u}} is equivalent to the value of {{c|v}}. | + | |The value of {{c|u}} is equivalent to the value of {{c|v}}. |
The value of {{c|v}} is unchanged. | The value of {{c|v}} is unchanged. | ||
|- | |- | ||
| − | | {{c|T(v)}} | + | |{{c|T(v)}} |
| − | | The value of {{c|T(v)}} is equivalent to the value of {{c|v}}. | + | |The value of {{c|T(v)}} is equivalent to the value of {{c|v}}. |
The value of {{c|v}} is unchanged. | The value of {{c|v}} is unchanged. | ||
|} | |} | ||
Revision as of 10:38, 8 August 2023
Specifies that an instance of the type can be copy-constructed from an lvalue expression.
Requirements
The type T satisfies CopyConstructible if
- The type
Tsatisfies MoveConstructible, and
Given
- v, an lvalue expression of type
Tor const T or an rvalue expression of type const T, - u, an arbitrary identifier.
The following expressions must be valid and have their specified effects:
| Expression | Post-conditions |
|---|---|
| T u = v; | The value of u is equivalent to the value of v.
The value of v is unchanged. |
| T(v) | The value of T(v) is equivalent to the value of v.
The value of v is unchanged. |
|
The expression v.~T() also must be valid, and, for lvalue v, the expression &v must have the type |
(until C++11) |
Notes
Until C++11, classes that overloaded operator& were not CopyConstructible and thus were not usable in the standard library containers. This is a design decision in C++98 (instead of a defect, see LWG issue 390).
Since C++11, the standard library uses std::addressof whenever the address of an object is needed.
See also
| (C++11)(C++11)(C++11) |
checks if a type has a copy constructor (class template) |
| (C++20) |
specifies that an object of a type can be copy constructed and move constructed (concept) |
