Re: RFC 118 (v1) lvalue subs: parameters, explicit assignment, andwantarray() changes

[Damian Conway]

   > Damian Conway writes:
   > >  pre mymethod : group("safe-coding practice") { @_ > 0 }
   > >  pre mymethod : group("debugging") { print @_, "\n"; }
   > 
   > Using these for lvalue subs doesn't give you the behaviour you want:
   > 
   >   sub foo :lvalue { $foo }
   >   post foo { die if $foo == 5 }
   > 
   >   eval {
   >     foo() = 5;
   >   };
   > 
   > Should not set the lvalue of foo to 5.  But you can't test for
   > bad values until after you've made the assignment.

Postconditions on lvalue subs are not tested until the end of the complete 
expression in which the sub is called.

Damian