Recursive inheritance detected while looking for method - Why

Trying out some object methods the other day I came across this error.

I'm wondering why this behaviour is possible. Forgive me if I don't 
illustrate this well as I'm not totally up with the correct lingo.

The way I see if you have:-

package a;
##base

package b
@ISA = qw( a );

package c
@ISA = qw( a );

package d
@ISA = qw( a );


This all runs smoothly. If you have an object of 'd' then it'll also 
look for methods in a then give up.
If you then update 'd' to also have 'c'.
push @ISA, 'c';

Looking for the objects method will first go to d, then a, then c, than 
needlessly back to a before it gives up.

If you then update 'd' to also have 'b'.
push @ISA, 'b';

Looking for the objects method will first go:-
d, a, c, a, b, a
And so on with needless re-checks in packages it's already been too.

Of course if you set 'a' ISA 'b', then it's going to go into an infinate 
loop and you'll get the "Recursive inheritance detected while looking 
for method" error.


What I don't understand is.. and forgive me if I'm missing something.. 
why doesn't the method lookup for an object remember which packages it's 
already been to and no recheck them. In the examples above wouldn't this 
be quicker? It would also allow recursive inheritance, which I'm 
guessing is a bad thing, but could be useful in places.


Lyle

• Recursive inheritance detected while looking for method - Why by Lyle