Dispatching and different types

[Phillip Durbin <durbin@killians.gsfc.nasa.gov>]

I am new to Ada and  was wondering, why doesn't Ada dispatching let you
use different inherited types? And of course how do you work  around
this ? For example if I have tagged type T, and two derived types A and
B (where A and B have different extensions) then procedure P(A,B) would
be  illegal, although P(T'CLASS,T'CLASS) is OK. The problem as I see it
is how do I get the functionality of P(A,B) from P(T'CLASS,T'CLASS),
when the operation to be performed needs both extensions of A and B. I
can't dispatch P(T,B) or P(A,T) with P(A,B) because both A and B are
derived types that are different. It seems to me it would be rather easy
to do a signature check to find the correct one. Am I missing some
obvious point here or is there some other feature in Ada that handles
this better?

 Phil Durbin
 durbin@killians.gsfc.nasa.gov