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

[Douglas Gregor]

On Oct 15, 2011, at 8:21 PM, John Freeman wrote:

>> +  /// Declaration for the closure type.
>> +  CXXRecordDecl *ClosureType;
>> 
>> This is just getType()->getAsCXXRecordDecl(), no?
> 
> To my knowledge, yes it is. I added the ClosureType member simply for caching. I saw you removed it. The same could be done for the Function member as well. Is the general policy to keep the AST classes as small as possible?

Yes, absolutely. Memory footprint is extremely important when compiling C++ code, so we try to keep our data structures small. We'll use extra storage if it provides a significant performance improvement, of course, but that's not likely the case here.

>> +  /// The temporary object resulting from evaluating the lambda expression,
>> +  /// represented by a call to the constructor of the closure type.
>> +  CXXConstructExpr *ClosureObject;
>> 
>> This makes me think that LambdaExpr should just be a subclass of CXXConstructExpr, because there's a lot of behavior we get "for free" for lambdas if it derives from CXXConstructExpr (such as proper handling of the temporary). It would require some twisting-around of the logic for building lambda expressions (in particular, the LambdaExpr wouldn't be built until the whole body had been parsed), but I think the result would be better.
> 
> How should we store the bits and pieces up until the body has been parsed? Should there be a separate data structure just to hold them that gets passed between Sema functions, or should there be members within Sema for things like CurLambdaIntroducer and CurLambdaMethod, or something else?


Check out BlockScopeInfo; you'll want something like that, to keep the stack of active lambdas available. It'll become extremely important once you start handling implicit captures.

	- Doug