[cfe-dev] replacing Statement/Expression

Ted Kremenek kremenek at apple.com
Sun Aug 17 13:11:25 PDT 2008

On Aug 17, 2008, at 12:52 PM, Rajesh Karmani wrote:

> Hello,
> Is there a facility to replace a statement or an expression with  
> another
> in the AST? In the scenario that I am looking at, the text replacement
> strategy doesn't work because after rewriting the child expression,  
> when
> I rewrite the parent expression it picks the child expressions from  
> the
> AST which do not reflect the "updated" child expression.

Hi Rajesh,

While we haven't fleshed out the use of setter methods for ASTs, one  
can indeed replace the AST nodes using Stmt::child_iterator  
interface.  child_iterator (which is a typedef of the class  
StmtIterator) actually returns a reference to the Stmt* contained  
within an AST node.  For example, here is a snippet from  

   // Start by rewriting all children.
   for (Stmt::child_iterator CI = S->child_begin(), E = S->child_end();
        CI != E; ++CI)
     if (*CI) {
       Stmt *newStmt = RewriteFunctionBodyOrGlobalInitializer(*CI);
       if (newStmt)
         *CI = newStmt;

We may gradually add direct setter methods to AST nodes as the  
refactoring API gets fleshed out (feel free to make suggestions and  
propose patches).  One thing we're still resolving is the memory  
management model for AST nodes.  Right now they are all created using  
new/malloc, but we've started rolling out changes that Stmt's are  
allocated using a memory allocator associated with the ASTContext  
object.  I don't think you have to worry about this for now, but it is  
something to be aware of (i.e., the API is still evolving).


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