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

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.

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.

Table 28 — NullablePointer requirements

Expression | Return type | Operational semantics |

P u(np); | Postconditions: u == nullptr | |

P u = np; | ||

P(np) | Postconditions: P(np) == nullptr | |

t = np | P& | Postconditions: t == nullptr |

a != b | contextually convertible to bool | !(a == b) |

a == np | contextually convertible to bool | a == P() |

np == a | ||

a != np | contextually convertible to bool | !(a == np) |

np != a |