[boost] Re: Collection concept

From: jsiek_at_[hidden]
Date: 2000-01-12 20:32:38

Dave Abrahams writes:
 > This is beautiful...
 > 

Thanks

 [ good part ... ]
 > 
 > ...up to this point...
 > 
 > > but only in contexts where there are not
 > > requirements for member access on the value type, since it is
 > > impossible for a proxy class to provide member access due to the lack
 > > of an overloadable member access operator.
 > 
 > C'mon, suppose I provide a reference type which reflects all of the members
 > of the value type that are required by the context?

Ok, good point.

 > > Also note it is
 > > permissable for the reference type to be the value type itself.  It
 > > would not be appropriate to use the reference type for a function
 > > argument with the intent that the argument will be pass-by-reference.
 > 
 > Hmm. There may be some subtle issues here, which I'd rather not discuss.
 > Against my better judgement:
 > 
 > If you return a proxy by value you can pass it to a function accepting a
 > const proxy&, but not to a function accepting a non-const proxy&. This would
 > only matter in the case where the reference type was identical to the value
 > type, since otherwise (in theory at least) the client code doesn't know
 > anything about the reference type.
 > 
 > Do you need two separate proxy types for const and non-const references?
 > 

Yes, often they do need to be different types. Also, sometimes you
don't need a proxy for the const reference, but you do for the
reference (this is the case for sparse vectors/matrices in MTL).
Good thing there are two different typedefs to handle this :)

Ciao,

Jeremy