Re: Member pointer to nested member
On 08.08.14 18.15, Victor Bazarov wrote:
I think the reason is that the member of X is not a member of Y. You
can't declare a pointer to member of Y and then extract the member of X
to do it. What you need is a type that would define the path *through*
an X member of Y, then *to* a member of that member.
Yes, that's it. But the result is binary compatible with Y::*. So I
assumed it should work. With inheritance it also works, although this
could be more complex in case of virtual inheritance.
In fact it works also if I cast the result of offsetof, but this is
highly UB and I don't want to do so.
If this is impossible any other ideas? (without the C style offsetof)
What is it you're trying to accomplish?
The outer struct carries a bundle of information of different categories
placed in inner structs.
I have functions that merge information of multiple structs into a
single one. These functions are data type specific and need to be
invoked for each (nested) field. But the function are invariant of the
inner struct and the field.
There are many fields (several dozens) and repeating the code (a dozen
lines) over and over is awful.
Can you flatten your Y struct?
Unfortunately not.
Parts of the program deal only with some of the inner structs. OK, I
could refactor that. But another bundle with /pointers/ to the inner
structs is also passed to the plug-in interface. So individual
categories could be extendend without breaking binary compatibility of
the plug-ins. The outer struct is not part of the public interface.
I could use inheritance to come around the restriction. Unfortunately
the field names are not unique, e.g. .flags comes more than once in the
inner structs.
Marcel