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[module.context] Instantiation context is inconsistently defined #3985

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sdkrystian opened this issue May 6, 2020 · 2 comments
Open

[module.context] Instantiation context is inconsistently defined #3985

sdkrystian opened this issue May 6, 2020 · 2 comments
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decision-required A decision of the editorial group (or the Project Editor) is required.

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@sdkrystian
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sdkrystian commented May 6, 2020 •
edited

The definition of instantiation context is as follows:

The instantiation context is a set of points within the program that determines which names are visible to argument-dependent name lookup and which declarations are reachable in the context of a particular declaration or template instantiation.

(side note: I'm pretty sure "template instantiation" should be "specialization" here)

We further go on to state:

In any other case, the instantiation context at a point within the program comprises that point.

The last bullet here seems to be inconsistent with the rest of the definition; we defined instantiation context to be relative to a declaration (or specialization), but then we specify what it is in the context of a program point.

Also, instead of "during the instantiation of [...]" we should say "in the context of [...]" as the lookup would be performed within the specialization/implicit definition.
@jensmaurer
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I think we intentionally refer to "template instantiation" (i.e. the act of producing a specialization), because that's a situation where name lookup happens (again). Once you have an instantiated specialization, name lookup is a thing of the past.

For the second issue, I'm not seeing it either. We say an instantiation context is a set of points, and we specify in an "otherwise" a set with a single element.

@sdkrystian
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@jensmaurer For the second issue, the problem there is not what we define instantiation context as, but the context for which we define it (i.e. for a point in the program, the instantiation context is [...])

Reachability (in [module.reach]) is defined as:

A declaration D is reachable if, for any point P in the instantiation context [...]

This doesn't provide a context (i.e. the program point) from which we are "getting" the instantiation context.

@jensmaurer jensmaurer added the decision-required A decision of the editorial group (or the Project Editor) is required. label Nov 6, 2020
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