20 Library introduction [library]

A NullablePointer type is a pointer-like type that supports null values. A type P meets the requirements of NullablePointer if:

• (1.1)

  P satisfies the requirements of EqualityComparable, DefaultConstructible, CopyConstructible, CopyAssignable, and Destructible,

• (1.2)

  lvalues of type P are swappable,

• (1.3)

  the expressions shown in Table 28 are valid and have the indicated semantics, and

• (1.4)

  P satisfies 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 value. [ Note: Operations involving indeterminate values may cause undefined behavior.  — end note ]

An object p of type P can be contextually 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 NullablePointer requirements shall exit via an exception.

In Table 28, 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.