This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-19

575. Criteria for deduction failure

[Voted into WP at August, 2010 meeting.]

The last two sentences of 13.10.3 [temp.deduct] paragraph 5 read:

When all template arguments have been deduced or obtained from default template arguments, all uses of template parameters in non-deduced contexts are replaced with the corresponding deduced or default argument values. If the substitution results in an invalid type, as described above, type deduction fails.

Shouldn't the substitution occur for all uses of the parameters, so that any of them could result in deduction failure?

Proposed resolution (October, 2006):

Change 13.10.3 [temp.deduct] paragraph 5 as follows:

...When all template arguments have been deduced or obtained from default template arguments, all uses of template parameters in non-deduced contexts the function type are replaced with the corresponding deduced or default argument values. If the substitution results in an invalid type, as described above, type deduction fails.

Notes from the September, 2008 meeting:

This issue was returned to "drafting" status in order to coordinate the wording with the concepts proposal.

Proposed resolution (March, 2010):

Change 13.10.3 [temp.deduct] paragraph 5 as follows:

When all template arguments have been deduced or obtained from default template arguments, all uses of template parameters in non-deduced contexts the template parameter list of the template and the function type are replaced with the corresponding deduced or default argument values. If the substitution results in an invalid type, as described above, type deduction fails.