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### 38. Facet definition incomplete

Section: 28.3.2 [locale.global.templates] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

It has been noticed by Esa Pulkkinen that the definition of "facet" is incomplete. In particular, a class derived from another facet, but which does not define a member id, cannot safely serve as the argument F to use_facet<F>(loc), because there is no guarantee that a reference to the facet instance stored in loc is safely convertible to F.

Proposed resolution:

In the definition of std::use_facet<>(), replace the text in paragraph 1 which reads:

> Get a reference to a facet of a locale.

with:

> Requires: `Facet` is a facet class whose definition contains the public static member `id` as defined in 28.3.1.2.2 [locale.facet].

[ Kona: strike as overspecification the text "(not inherits)" from the original resolution, which read "... whose definition contains (not inherits) the public static member `id`..." ]