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[basic.def.odr] p5 "appears as" is not defined and "named by" is a better choice #5533

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xmh0511 opened this issue Jun 17, 2022 · 5 comments · Fixed by #5534
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[basic.def.odr] p5 "appears as" is not defined and "named by" is a better choice #5533

xmh0511 opened this issue Jun 17, 2022 · 5 comments · Fixed by #5534

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@xmh0511
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xmh0511 commented Jun 17, 2022

[basic.def.odr] p5 says

A variable is named by an expression if the expression is an id-expression that denotes it. A variable x whose name appears as a potentially-evaluated expression E is odr-used by E unless

The intent of what E is here refers to the id-expression naming the entity. "appear as" is not a defined meaning. It is better that we just say:

A variable is named by an expression if the expression is an id-expression that denotes it. A variable x named by a potentially-evaluated expression E is odr-used by E unless

It is more clear.
@jensmaurer
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No, because it raises the question whether an unevaluated subexpression (e.g. sizeof) of a potentially-evaluated expression also fits "named by". (It clearly doesn't fit "appears as".)

@xmh0511
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xmh0511 commented Jun 17, 2022 •
edited

No, because it raises the question whether an unevaluated subexpression (e.g. sizeof) of a potentially-evaluated expression also fits "named by". (It clearly doesn't fit "appears as".)

Why? Did you mean such as this example?

auto c = sizeof(T::x);

The variable T:x is not named by the expression sizeof(T::x), it is just named by T::x that is an id-expression that denotes it. T::x is not potentially evaluated since it is the operand of sizeof. Could you please give a counterexample?

Furthermore, the wording about whether a function is odr-used in N495 has been changed from

A function whose name appears as a potentially-evaluated expression is odr-used if

to

A function is odr-used if it is named by a potentially-evaluated expression or conversion.

What's the difference if we apply a similar change for variables?

@jensmaurer
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Agreed.

@xmh0511
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xmh0511 commented Jun 17, 2022

#5534

@tkoeppe
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tkoeppe commented Sep 8, 2022

@jensmaurer Could you take a look at #5534 then?

@tkoeppe tkoeppe mentioned this issue Sep 8, 2022
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use "named by" in place of "appear as" for odr-using a variable
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@tkoeppe @xmh0511 @jensmaurer