4.8 KiB
[nullablepointer.requirements]
16 Library introduction [library]
16.4 Library-wide requirements [requirements]
16.4.4 Requirements on types and expressions [utility.requirements]
16.4.4.4 Cpp17NullablePointer requirements [nullablepointer.requirements]
A Cpp17NullablePointer type is a pointer-like type that supports null values.
A type P meets the Cpp17NullablePointer requirements if
P meets the Cpp17EqualityComparable,Cpp17DefaultConstructible, Cpp17CopyConstructible, Cpp17CopyAssignable,Cpp17Swappable, and Cpp17Destructible requirements,
the expressions shown in Table 36 are valid and have the indicated semantics, and
P meets all the other requirements of this subclause.
A value-initialized object of type P produces the null value of the type.
The null value shall be equivalent only to itself.
A default-initialized object of type P may have an indeterminate or erroneous value.
[Note 1:
Operations involving indeterminate values can cause undefined behavior, and operations involving erroneous values can cause erroneous behavior ([basic.indet]).
â end note]
An object p of type P can becontextually converted to bool.
The effect shall be as if p != nullptr had been evaluated in place of p.
No operation which is part of the Cpp17NullablePointer requirements shall exit via an exception.
In Table 36, u denotes an identifier, t denotes a non-const lvalue of type P, a and b denote values of type (possibly const) P, and np denotes a value of type (possibly const) std::nullptr_t.
Table 36 — Cpp17NullablePointer requirements [tab:cpp17.nullablepointer]
| ð Expression |
Return type | Operational semantics |
|---|---|---|
| ð P u(np); |
Postconditions: u == nullptr | |
| ð P u = np; |
||
| ð P(np) |
Postconditions: P(np) == nullptr | |
| ð t = np |
P& | Postconditions: t == nullptr |
| ð a != b |
decltype(a != b) models boolean-testable | !(a == b) |
| ð a == np |
decltype(a == np) and decltype(np == a) each model boolean-testable | a == P() |
| ð np == a |
||
| ð a != np |
decltype(a != np) and decltype(np != a) each model boolean-testable | !(a == np) |
| ð np != a |