Re: RFC 188 (v1) Objects : Private keys and methods

[Damian Conway]

   > >  print keys %hash, "\n";
   > >  exists $hash{key}{subkey};
   > >  print keys %hash, "\n";
   > 
   > >Or did that get fixed when I wasn't looking?
   > 
   > No, the -> operator has not been changed to do lazy evaluation.

That's not required. All that is necessary is for C<exists> nodes
in the op tree to propagate a special non-autovivifying context to 
subordinate nodes.

E.g. exists $hash{key}{subkey}

                exists
                   \
                  entry
                  /   \
              entry   "subkey"
              /   \
          %hash   "key"


Is preprocessed to:

                exists
                   \
                  entry(na)
                  /       \
              entry(na)   "subkey"
              /      \
          %hash(na)  "key"

which prevents %hash from autovivifying, which causes the left-most
branch to fail (without autovivifying) when asked for "key", which in
turn causes the entire <exists> to fail without autovivifying.


   > I just don't like reading "exists causes autovivification" when it
   > doesn't.

Sorry, I was being philosophically sloppy. A call to C<exists> can
*result* in autovivification (of something), though it does not itself
*cause* autovivification.

;-)


Damian