CWG Issue 393 (original) (raw)

This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-04-13

393. Pointer to array of unknown bound in template argument list in parameter

Section: 9.3.4.6 [dcl.fct]Status: CD4Submitter: Mark MitchellDate: 12 Dec 2002

[Moved to DR at the November, 2014 meeting.]

EDG rejects this code:

template struct S {};

void f (S<int (*)[]>);

G++ accepts it.

This is another case where the standard isn't very clear:

The language from 9.3.4.6 [dcl.fct] is:

If the type of a parameter includes a type of the form "pointer to array of unknown bound of T" or "reference to array of unknown bound of T," the program is ill-formed.

Since "includes a type" is not a term defined in the standard, we're left to guess what this means. (It would be better if this were a recursive definition, the way a type theoretician would do it:

• Every type includes itself.
• T* includes T
• T[] includes T
• ... )

Notes from April 2003 meeting:

We agreed that the example should be allowed.

Additional note (January, 2013):

Additional discussion of this issue has arisen . For example, the following is permissible:

T (p) [] = (U()[])0;

but the following is not:

template void sp_assert_convertible( T* ) {}

sp_assert_convertible<T[]>( (U(*)[])0 );

Proposed resolution (February, 2014):

Change 9.3.4.6 [dcl.fct] paragraph 8 as follows, including deleting the footnote:

If the type of a parameter includes a type of the form “pointer to array of unknown bound of T” or “reference to array of unknown bound of T,” the program is ill-formed.101 Functions shall not have a return type of type array or function, although...