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### 3421. Imperfect ADL emulation for `boolean-testable`

Section: 18.5.2 [concept.booleantestable] Status: WP Submitter: Davis Herring Opened: 2020-03-24 Last modified: 2020-11-09

Priority: 0

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Discussion:

18.5.2 [concept.booleantestable]/4 checks for "a specialization of a class template that is a member of the same namespace as `D`", which ignores the possibility of inline namespaces.

[2020-04-18 Issue Prioritization]

Status set to Tentatively Ready after six positive votes on the reflector.

[2020-11-09 Approved In November virtual meeting. Status changed: Tentatively Ready → WP.]

Proposed resolution:

This wording is relative to N4861.

1. Modify 18.5.2 [concept.booleantestable] as indicated:

   > -4- A key parameter of a function template `D` is a function parameter of type cv `X` or reference thereto, where `X` names a specialization of a class template that has the same innermost enclosing non-inline is a member of the same namespace as `D`, and `X` contains at least one template parameter that participates in template argument deduction. […]