This is the mail archive of the mailing list for the GDB project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: MI and anonymous unions

Support for anonymous unions & structures is another of the "things we fixed but haven't submitted back"... We do pretty much what Vladimir suggests, though I use #anon#N for the varobj name: the choice doesn't much matter. We still return a blank expression (since that's really what the There's one other tricky bit 'caused by the fact that you might have more than one anonymous union or structure inside a structure. This wouldn't be a problem, but the varobj code tends to look up structure elements by name, which obviously won't work here. So you have to convert all the code that looks up structure elements to use the index rather than the name.

Another of the things we do in our varobj code for C++ is that we look up the dynamic type of objects (the same mechanism that "set print object on" uses, and the value & children we return are based on the dynamic type. As soon as you do that, you really do need a "give me the expression that can recreate this varobj" for child varobj's. Otherwise the MI client needs to get all these dynamic casts right to get down to the proper child, which is a bit of a pain.

But it's a generally useful command. We called it "var-info-path- expression" and given a varobj, it returns the expression that if evaluated would result in the same value. Xcode uses this for "show in separate window" actions in the debugger variable view. You can also use the to eliminate the "." for the anonymous structures or unions - though of course the MI client could do this too...


On Nov 15, 2006, at 6:58 AM, Vladimir Prus wrote:

Daniel Jacobowitz wrote:

On Wed, Nov 15, 2006 at 12:38:16PM +0300, Vladimir Prus wrote:
Traversing it with MI eventually gives:

-var-list-children V.public

^ done ,numchild="1",children=[child={name="V.public.",exp="",numchild="1",
                 type="union {...}"}]
    -var-list-children V.public.
     -var-list-children V.public..public

Although this kinda works, I'm pretty sure UI won't be happy about empty
expression for a variable object, and if you have two anonymous unions,
you can't even address them.

I'm not sure what to do for the empty expression. There's nothing we can put there which would act like a named union, since you need one less period - hmm, we were just discussing an MI command to recreate expressions the other day...

How do people use the exp="" result? Should it be "<anonymous>"?

KDevelop uses it to construct the full expression, which will obviously
break. I'm not sure about Eclipse, I think it does the same.

But given that there's no way to put anything there that can be used to
recreate expression, I don't see much difference. "<anonymous>" would work
better if this is to be shown in some UI, I think.

How about using some unique identifier for variable objects corresponding
for anonymous unions? Say "@N"?

That sounds reasonable.


- Volodya

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]