Re: same-address mappings vs. relative pointers

On 2013-12-05 15:44:34 +0100, Andres Freund wrote:
> On 2013-12-05 07:44:27 -0500, Robert Haas wrote:
> > And then I thought, boy, it sucks
> > not to be able to declare what kind of a thing we're pointing *at*
> > here, but apart from using C++ I see no solution to that problem.  I
> > guess we could do something like this:
> >
> > #define relptr(type)   Size
> >
> > So the compiler wouldn't enforce anything, but at least notationally
> > we'd know what sort of object we were supposedly referencing.
> 
> There might be some ugly compiler dependent magic we could do. Depending
> on how we decide to declare offsets. Like (very, very roughly)
> 
> #define relptr(type, struct_name, varname) union struct_name##_##varname{ \
>     type relptr_type; \
>     Offset relptr_off;
> }
> 
> And then, for accessing have:
> #define relptr_access(seg, off) \
>   typeof(off.relptr_type)* (((char *)seg->base_address) + off.relptr_off)
> 
> But boy, that's ugly.

On second thought - there's probably no reason to name the union, making
it somewhat less ugly.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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