GB046 07.05.4 Allow caching of evaluations of concept specializations

[wg21bot]

Implementations should be allowed to cache the results of concept specialisation evaluations
The current wording of [expr.prim.id]/4 precludes the possibility of caching concept specialisations (which has led to demonstrable performance issues in implementations that are standard-conforming contrasted against implementations that cache results).

Proposed change:
Add wording to the effect of:
A program which causes a given set of template arguments to change their satisfaction of a constraint, and relies upon this change, is ill-formed, no diagnostic is required.

[jfbastien]

Not enough information, Christopher Di Bella to come back with information.

[jfbastien]

EWG Prague Tuesday morning:

Add wording to the effect of: A program which causes a given set of template arguments to change their satisfaction of a constraint, and relies upon this change, is ill-formed, no diagnostic is required.

SF	F	N	A	SA
10	14	0	2	0

Andrew, Gaby, and Roger to write paper.

[jfbastien]

EWG Prague Tuesday after lunch:

Adopt D2104 as a resolution to GB046, send to Core.

SF	F	N	A	SA
9	8	1	0	0

[jensmaurer]

CWG in Prague: Accepted with modification. See paper P2104R0.