My understanding of the semantic of pairs as in A6: A pair in a given scalar context should return its first element coerced to match the said context.
This seems to be a prerequisite to use pairs as function arguments. Example with the boolean context: bool $b = a => 10; # $b == 1 But what about C<Scalar>, C<Ref> and C<string> contexts? I expect an object to return a reference to itself in Ref Context. I have trouble to remember if assignation in Scalar context gives a reference to the assigned object, or its size. I expect that assigning a to string gets me a string that can usually get evaluated to return a value equal to the the original one. In the three cases where I assume to have described the nornal semantic, I don't get a behavior compatible with my understanding of pairs used as arguments. To solve that dilemma, can we just say that pairs used as arguments is a special case. Now let's talk about the implementation of perl pairs and lisp pairs as a PMC, assuming pairs as arguments is a special case. We need both the normal pair semantic and the one about arguments as pairs. This mean that the argument as pair is implemented as keyed PMC methods. I propose special methods to avoid that overhead. They are the moral equivalent of the lisp car and cdr in a language with context. These methods would be: (get|set)_first_(integer|number|bool|pmc) (get|set)_second_(integer|number|bool|pmc) Note that they can be used as optimization for array pmcs, Now I run in a second problem that I have already touched on perl6-internal. For storage optimization purposes, I want to avoid as possible to use pmcs for pairs elements. Say I set the key is an int (they can be in Perl6?), I want to avoid to promote it to a PMC. But I must do it if one takes a reference to that key. This happens if someone does a get_first_pmc() or a get_second_pmc(). But sometimes one would just access a pmc to clone it. This does not mean that a reference is really taken and that there is no need to promote the element to a pmc. So we need a clone_first() and a clone_second() to avoid unecessary element promotion. More generally, in pmcs that act as composite containers which elements are not necessarily pmc, we need these cloning methods as well: PMC* clone_pmc_keyed(PMC* key) PMC* clone_pmc_keyed_int(INTVAL key) PMC* clone_pmc_keyed_str(STRING* key) Comments? -- stef
