r180127 - [libclang] Introduce a CXCursor_ObjCSelfExpr cursor, which is the equivalent of CXCursor_CXXThisExpr for C++ code.

[Jordan Rose]

On Apr 23, 2013, at 13:46 , Argyrios Kyrtzidis <akyrtzi at gmail.com> wrote:

> On Apr 23, 2013, at 12:37 PM, Jordan Rose <jordan_rose at apple.com> wrote:
> 
>> 
>> On Apr 23, 2013, at 12:16 , Argyrios Kyrtzidis <akyrtzi at gmail.com> wrote:
>> 
>>> On Apr 23, 2013, at 12:03 PM, Jordan Rose <jordan_rose at apple.com> wrote:
>>> 
>>>> Sorry, why is this right way to implement this? 'self' is very deliberately not a special kind of expression in Objective-C. Why not expose this on the associated ParmVarDecl instead?
>>> 
>>> What is the advantage with that approach ? Whether there is a ParmVarDecl or not seems like an implementation detail of the AST. If you are worried that there is one more cursor to consider, I'd argue the same applies for CXCursor_CXXThisExpr.
>> 
>> CXXThisExpr matches the AST, which matches the C++ standard. There is no Objective-C standard, but certainly 'self' is not treated specially in most cases.
> 
> Hmm, since 'self' is not declared anywhere in the source, I consider it somewhat "special".
> 
>> 
>> I can't put my finger on it, but it makes a lot more sense to me to say "is this variable 'self'?"
> 
> What are you suggesting exactly, have "self" be a reference of a CXCursor_ParmDecl and introduce a libclang function to answer "is this parameter 'self'" ?
> 
> AFAIK you'd only get such a variable via a "'self' ref expression"; there is no other case where libclang is going to return such a thing, so such a function has limited utility.
> And unless we start exposing "self" as a CXCursor_ParmDecl "child" of a method (which I don't like) it seems inconsistent that we would report as referenced a ParmDecl that we never reported before in the source.

Hm. That's different from the Clang ASTs. I guess you don't have a Decl for _cmd either?

But that makes sense—returning a Decl you won't see any other way doesn't feel consistent.

Now if you had something like liveness analysis, or "find all variables of this type", then it might be interesting to have 'self' as an explicit Decl. 


>> than "is this expression 'self'?", especially in init methods where 'self' can be reassigned. 'this' can never be reassigned.
> 
> Not sure why CXCursor_ObjCSelfExpr conflicts with 'self' getting reassigned ?

It doesn't, but it seems funny to me to think of it as a special type of expression when it accepts assignment. Then again, so do ObjCPropertyRefExprs.

Actually, it could be important for dependency analysis questions: "what variables might affect the value of this expression?". But now I'm talking about potential future APIs as justification for a decision now, which might not be worth it.

Jordan

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