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[basic.lookup.unqual] Component names in converstion-type-id are unqualified names? #4812

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xmh0511 opened this issue Aug 14, 2021 · 2 comments · Fixed by #4813
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[basic.lookup.unqual] Component names in converstion-type-id are unqualified names? #4812

xmh0511 opened this issue Aug 14, 2021 · 2 comments · Fixed by #4813
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@jensmaurer

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@xmh0511
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xmh0511 commented Aug 14, 2021 •
edited

[basic.lookup.unqual] p5

An unqualified name that is a component name ([expr.prim.id.unqual]) of a type-specifier or ptr-operator of a conversion-type-id is looked up in the same fashion as the conversion-function-id in which it appears. If that lookup finds nothing, it undergoes unqualified name lookup; in each case, only names that denote types or templates whose specializations are types are considered.

The rule says these components names are called unqualified names, which has conflicted with [basic.lookup.unqual] p4

An unqualified name is a name that does not follow a nested-name-specifier or the . or -> in a class member access expression ([expr.ref]), possibly after a template keyword or ~. Unless otherwise specified, such a name undergoes unqualified name lookup from the point where it appears.

Consider the example after [basic.lookup.unqual] p5

X().operator U T::*();  // #1
X().operator U decltype(T())::*();  //#2

The names U and T in these two expressions all follow . in their class member access expressions. Hence, they shouldn't be unqualified names. Could we change the unqualified name in [basic.lookup.unqual] p5 to name:

A name that is a component name...

Except for that, [basic.lookup.unqual] p5 also does not specify how will the lookup perform on these names that are not component names. Such as the T that appears in decltype(T()) in #2, it is not the component name of neither a type-specifier nor ptr-operator of a conversion-type-id. Which kind of lookup will perform on that name?
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jensmaurer commented Aug 14, 2021 •
edited

The rule says these components names are called unqualified names

No, the rule says that a certain subset of unqualified names gets special treatment.

So, I see two concerns in treatment of X().operator U decltype(T())::*():

First, your reading of the definition of "unqualified name" and "follow" says that "U" follows the "." in a class member access expression and thus is not an unqualified name. I think the interpretation here is "immediately follow", and we can fix that by saying so.

Applying your suggested change "unqualified name" -> "name" is not good, because we don't want to change the lookup rules for qualified names inside a conversion-type-id.

Second, for decltype(T()), "T" is obviously an unqualified name without a special rule, so "Unless otherwise specified, such a name undergoes unqualified name lookup from the point where it appears." applies.

@jensmaurer jensmaurer mentioned this issue Aug 14, 2021
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@jensmaurer jensmaurer changed the title Component names in converstion-type-id are unqualified names? [basic.lookup.unqual] Component names in converstion-type-id are unqualified names? Aug 14, 2021
@jensmaurer jensmaurer self-assigned this Aug 14, 2021
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xmh0511 commented Aug 16, 2021

Yes, just "immediately follow" would clean the two concerns.

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[basic.lookup.unqual] Clarify 'unqualified name' jensmaurer/draft
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