[boost] iterator_category> algorithm selection with cast operator

Subject: [boost] iterator_category> algorithm selection with cast operator
From: gzp (z.p.gaal_at_[hidden])
Date: 2010-06-25 11:11:28

Hello,

I've read the article of ranges vs. iterators from Andrei Alexandrescu and
I've start to implement something similar and wanted to extend the idea to
2D grids (popFront, front, popLine).

OK, I now s/g similar can be achieved using iterators(ranges) returning
iterators(ranges) as the current item, I was just simple experimenting.

Using the iterator_category concept empty structs are used to check, select
functions at compile time.
struct A {};
struct B : A {}
void foo( A ) { alg1... }
void foo( B ) { alg2... specialized for B }
template<typename T> void foofoo( T ){ foo( getCategory<T>() ); } 

My first idea was to use multiple inheritance, but it result error
(ambiguous call)
struct A {};
struct B : A {};
struct A2 : A {};
struct B2 : A2, B {};

void foo( A ) { alg1... }
void foo( B ) { alg2... specialized for B }
void foo( A2 ) { alg3... specialized for A2 }
void g()	{ B2 b; f(b); } // error: is it f(B) or f(A2)

Than I've used cast operators and inheritance stating that, a B2 is mainly
an A2 and secondly a B:
struct A {};
struct B : A {};
struct A2 : A {};
struct B2 : A2 { operator B() { return B(); } };

void foo( A ) { alg1... }
void foo( B ) { alg2... specialized for B }
void foo( A2 ) { alg3... specialized for A2 }
void g()	{ B2 b; f(b); }  // shall call f(A2)

So my question is that, is it a working method, or the whole concept is
wrong ?
Has anyone used something similar ? If so, is there some sample
codes/results?

Thank you, 
Gzp

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