Re: [MI] lvalues and variable_editable

[Daniel Jacobowitz <drow@false.org>]

On Tue, Jun 26, 2007 at 11:36:16PM +1200, Nick Roberts wrote:
> 
> I've been wondering what the difference is between varobj_value_is_changeable_p
> and variable_editable.  Recent discussion on the gdb mailing list makes
> me think that, in essence, a value is only changeable but not editable when
> it's an lvalue -- but currently varobj.c doesn't capture this difference.
> 
> Here are two experimental patches:
> 
> 1) varobj.c: Test if the value of variable object is an lvalue.  I think this
>    can only occur for root values.

I'm still a bit confused but I think this is because I read "lvalue"
and think of the C language meaning.  An lvalue is something which can
occur on the left hand side of an assignment.  So it can happen for
children too, for instance.

Right now a value is "changeable" unless it is a fake child
(e.g. "public"), a struct, a union, or an array.  This makes some
sense since the value we print out for those cases is not useful for
editing.  For instance "{...}".  Their children will, I believe, be
changeable.

A value is editable in C unless it is a struct, union, array,
function, or method.  C++ adds the fake access children again.

So the only things which are editable but not changeable are functions
and methods.  That doesn't seem like a useful distinction.

Back in revision 1.1, fake children and structs and unions were not
changeable.  Those and arrays, functions, methods, and members were
not editable.  That doesn't make considerably more sense to me either.

The difference in usage seems to be that we forbid attempts to modify
non-editable variables, and we omit reporting changes for
non-changeable variables.

> It would seem sensible to define variable_editable using
> varobj_value_is_changeable_p and I don't think language dependent versions
> aren't needed.

I agree.  But is there anything which should be one and not the other?
Maybe we can dispense with changeable entirely.

-- 
Daniel Jacobowitz
CodeSourcery