4155. Cpp17NullablePointer should require that some expression can be contextually converted to bool

Section: 16.4.4.4 [nullablepointer.requirements] Status: New Submitter: Jiang An Opened: 2024-09-18 Last modified: 2024-10-02

Priority: 3

View all other issues in [nullablepointer.requirements].

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Discussion:

Currently, 16.4.4.4 [nullablepointer.requirements]/3 requires "An object p of type P can be contextually converted to bool", while the core language wording (7.3.1 [conv.general]/4) only says some expressions can be contextually converted to bool. Moreover, the value category and cv-qualification are not mentioned, presumably both non-const and const P, together with all value categories are expected.

[2024-10-02; Reflector poll]

Set priority to 3 after reflector poll.

"This is an improvement, but judging from microsoft/STL 4964, I think we actually want to define a "contextually-boolean-testable" for this."

Proposed resolution:

This wording is relative to N4988.

1. Modify 16.4.4.4 [nullablepointer.requirements] as indicated:

   -3- 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.

2. Add a row to the bottom of [tab:cpp17.nullablepointer]:

   Expression	Return type	Operational semantics
   ...	...	...
   a ? true : false	bool	a != np