[cfe-dev] Question of RecursiveASTVisitor class

[Nikola Smiljanic]

There are two parent-child relationships at play.

1. Traverse method visits AST nodes that form a tree. CXXRecordDecl is the
parent of each of its CXXMethodDecls and FieldDecls. This is what you'll
see with clang -cc1 -ast-dump
2. WalkUpFrom method visits the class hierarchy of a single AST node.
CXXRecordDecl inherits RecordDecl which inherits TagDecl etc. Think of
serialization, to serialize CXXRecordDecl you'd first want to serialize
everything from the base class and so on recursively.

On Mon, Nov 3, 2014 at 12:32 PM, Xiaohui Chen <xchen422 at uwo.ca> wrote:

>  Dear all:
>
> My name is Xiaohui Chen, a computer science student in UWO in canada and i
> am using Clang as the frontend of my project, but i am confusing of the
> following statements.
> PS: i am a newbie.
>
> These tasks are done by three groups of methods, respectively:00089 ///   1. TraverseDecl(Decl *x) does task #1.  It is the entry point00090 ///      for traversing an AST rooted at x.  This method simply00091 ///      dispatches (i.e. forwards) to TraverseFoo(Foo *x) where Foo00092 ///      is the dynamic type of *x, which calls WalkUpFromFoo(x) and00093 ///      then recursively visits the child nodes of x.00094 ///      TraverseStmt(Stmt *x) and TraverseType(QualType x) work00095 ///      similarly.00096 ///   2. WalkUpFromFoo(Foo *x) does task #2.  It does not try to visit00097 ///      any child node of x.  Instead, it first calls WalkUpFromBar(x)00098 ///      where Bar is the direct parent class of Foo (unless Foo has00099 ///      no parent), and then calls VisitFoo(x) (see the next list item).00100 ///   3. VisitFoo(Foo *x) does task #3.00101 ///00102 /// These three method groups are tiered (Traverse* > WalkUpFrom* >00103 /// Visit*).  A method (e.g. Traverse*) may call methods from the same00104 /// tier (e.g. other Traverse*) or one tier lower (e.g. WalkUpFrom*).00105 /// It may not call methods from a higher tier.
>
> According to the above statement, the calling relationship between these
> functions are organized in this way in general:
>
> Traversal*()
> {
>         .......
>         WalkUpFrom*();
>         .......
> }
>
> WalkUpFrom*()
> {
>          .......
>          Visit*();
>          .......
>
> }
>
> am i right?
>
> For this statement:
>
> 00096 ///   2. WalkUpFromFoo(Foo *x) does task #2.  It does not try to visit00097 ///      any child node of x.  Instead, it first calls WalkUpFromBar(x)00098 ///      where Bar is the direct parent class of Foo (unless Foo has00099 ///      no parent), and then calls VisitFoo(x) (see the next list item).
>
> what do you mean by saying "the direct parent class of Foo"?
> why i need to visit the parent class before i visit the current class?
> what is the purpose? Could you please give me a short example?
>
> Thank you in advance!
>
> Sincerely
> xiaohui
>
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