Re: [Boost-users] checking validity

From: Fernando Cacciola (fernando_cacciola_at_[hidden])
Date: 2006-08-03 09:31:36

Ovanes Markarian wrote:
> Hello all,
> 
> I have one specific question. Which I am uncertain if it can be solved anyway.
> 
> 
> Imagine the following class structure:
> 
> 
> struct A
> {
> 	some_field* x;
> };
> 
> 
> struct B
> {
> 	optional<A>		a_;
> };
> 
> 
> struct C
> {
> 	optional<B>		b_;
> };
> 
> 
> Now I have an instance of struct C and would like to know if x is a valid pointer.
> 
> this code is really ugly:
> 
> if(c.b_)
> 	if(c.b_.a_)
> 		if(c.b_.a_.x)
> 			//do smth ...
> 
> 
If you need to access x form c (which is what are effectively doing 
here) then you should provide an accessor to x in c itself (and in B by 
transition).

struct B
{
   some_field* x() { return a_ ? a_->x : 0 ; }

   optional<A> a_;
};

struct C
{
   some_field* x() { return a()->x() ; }

   // this could be private
   optional<A> a() { return b_ ? b_->a_ : none ; }

   optional<B>  b_;
};

if ( c.x() )
   ....

HTH

Fernando Cacciola
fcacciola.50webs.com