[cfe-dev] Quick Questions: DeclRefExpr, TypedefDecl, TypedefType, and TemplateTypeParmDecl.

Douglas Gregor dgregor at apple.com
Tue Feb 8 09:31:19 PST 2011

On Feb 8, 2011, at 9:12 AM, Larisse Voufo wrote:

> 1 - The documentation for DeclRefExpr says the following:
>       "A reference to a declared variable, function, enum, etc."
>       Does this mean that DeclRefExprs also refer to types such as a concept's associated type 
>       (declared with the typename keyword, as a TemplateTypeParmDecl) ?

No. Look at the declaration hierarchy: DeclRefExpr stores a value (ValueDecl), but types are TypeDecls. Plus, a type reference is never an expression in the C family of languages.

> 2 -  How are TypedefTypes related to TypedefDecls, and possibly TemplateTypeParmDecl as well?

TypedefType it's a reference to a TypedefDecl that occurs in the source. You can create a small file that has a typedef and refers to it, then look at the generated AST, to see how it works.

TemplateTypeParmDecl is a bit messier, since the corresponding TemplateTypeParmType refers to depth/index rather than a specific declaration. We'd like it to refer to the declaration at some point in the future, but we're not there yet.

> 3-   I ran into this confusion when I was trying to modify the transformations on calls to concept's associated 
>       functions and types. I can't decide which one of these methods would be the most appropriate or general 
>       place for the change: TransformDeclRefExpr, or TransformDecl and TransformType (and/or even    
>       TransformNestedNameSpecifier).
>       Basically, I'm trying to say: if the referred type or function (or variable) we are trying to transform is 
>       declared within a concept defn context, then match it to the appropriate concept map, and change 
>       the type or expression so that it now refers to the corresponding type or function (or variable) as defined
>       within the map context…

The cleanest approach is probably just to create a new Type for references to associated types; then you can transform that associated type reference specifically.

	- Doug

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