Are [basic.lookup.elab]/2 and [basic.scope.pdecl](7.2) in contradiction

[Ayrosa]

The apparent contradiction stems from the highlighted text in these two paragraphs

[basic.lookup.elab]/2:

If the elaborated-type-specifier has no nested-name-specifier, and unless the elaborated-type-specifier appears in a declaration with the following form:

class-key attribute-specifier-seqopt identifier ;

the identifier is looked up according to [basic.lookup.unqual] but ignoring any non-type names that have been declared.

 

If the elaborated-type-specifier is introduced by the enum keyword and this lookup does not find a previously declared type-name, the elaborated-type-specifier is ill-formed.

 

If the elaborated-type-specifier is introduced by the class-key and this lookup does not find a previously declared type-name, or if the elaborated-type-specifier appears in a declaration with the form:

class-key attribute-specifier-seqopt identifier ;

the elaborated-type-specifier is a declaration that introduces the class-name as described in [basic.scope.pdecl].

[basic.scope.pdecl]/(7.2):

for an elaborated-type-specifier of the form

class-key identifier

if the elaborated-type-specifier is used in the decl-specifier-seq or parameter-declaration-clause of a function defined in namespace scope, the identifier is declared as a class-name in the namespace that contains the declaration; otherwise, except as a friend declaration, the identifier is declared in the smallest namespace or block scope that contains the declaration.

 

[ Note

: 

These rules also apply within templates.

 — end note

 ]

 

[ Note

: 

Other forms of elaborated-type-specifier do not declare a new name, and therefore must refer to an existing type-name.

 

See [basic.lookup.elab] and [dcl.type.elab].

 — end note

 ]

The reason for this post came from this question of mine in Stackoverflow., more specifically from the answer by Barry and my comment to his answer.

[Brian Bi]

[basic.scope.pdecl]/7 begins "The point of declaration for a class first declared in an elaborated-type-specifier is as follows:"

In your question, the use of the elaborated-type-specifier in the declaration `void f(struct S&);` in the second snippet does not declare the class name because the lookup finds a previously declared type-name (according to [basic.lookup.elab]/2), so [basic.scope.pdecl]/7 doesn't apply.

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Brian Bi

[Ayrosa]

I took me sometime to really grasp what you wrote below. Thanks for the excellent answer.