[cfe-commits] [PATCH] Sema and AST for C++0x Lambda Expressions

[Douglas Gregor]

On Aug 14, 2011, at 1:50 PM, John Freeman wrote:

> On 8/12/11 5:26 PM, Douglas Gregor wrote:
>> +/// LambdaDecl - Represents a C++0x lambda expression.
>> +class LambdaDecl : public Decl, public DeclContext {
>> 
>> It would help if the comment here showed an example lambda expression, and pointed out the main pieces (capture list, body, etc.).
>> 
>> Please add more source-location information to LambdaDecl, so we have at least enough source-location information to implement getSourceRange() for LambdaDecl, covering the entire declaration. We'll need this source information for diagnostics and indexing.
>> 
>> +/// LambdaExpr - Adaptor class for mixing a LambdaDecl with expressions.
>> +class LambdaExpr : public Expr {
>> +  LambdaDecl *Lambda;
>> +
>> 
>> It's really not just an "adaptor", is it? It's the actual lambda expression. Please expand the comment with an example lambda expression. The commenting here is actually more important than for LambdaDecl, since lambdas are an expression in the language.
> 
> 
> Yeah, I'm still trying to figure out the LambdaDecl/LambdaExpr distinction myself. I based it off of the BlockDecl/BlockExpr design. Here is my current theory: LambdaExpr should be the AST node returned from ParseLambdaExpression. It holds a LambdaDecl that contains all the declarations related to the lambda expression: Captures, CXXMethodDecl, CXXRecordDecl. Location information for the whole expression will be stored in LambdaExpr. Components will have their location information stored in their respective Captures, ParmVarDecls, Stmt, etc.
> 
> I'm starting to wonder, though, if we even need a LambdaDecl. Why not just put everything in the LambdaExpr? I have not come across a need for a Decl or DeclContext for lambdas, but I might have just not hit it yet.


Interesting. The reasons for BlockDecl that I can think of really don't apply to lambdas, because lambdas already have a Decl and DeclContext associated with them (the generated CXXMethodDecl). It would certainly feel simpler to just have a LambdaExpr.

	- Doug