> Costs that seem to leap out from Christian's mutual-asymmetric multimethod > proposal: > > 1. Two lookups, "this+" and "+this", required. > 2. Intersection. > > (2) looks like a transformation or simplification of standard multimethod > Class Precedence List usage to find the most specific method. Any system > allowing multiple methods for a given operator will have something like it. > > (1) seems avoidable, though -- *assuming* it is not a phantom cost. We have > to deal with the symmetric vs. encapsulated issue, though. But notice that > Christian's proposal does not use "this" in the method bodies!
The really nice thing about this from a cost standpoint is that it caches well. If changes to the operators understood by an object are reflected in the object's hidden class (to use v8 terminology) the same way changes to methods are, all the same caching techniques can be used. A global (hidden class, hidden class, operator)->function cache can be used to ensure that the full operator resolution only has to be done once for any operand type pair, after which the result can be fetched by a simple hash table lookup. Similarly, inline caching can ensure that the hash lookup only has to be done once for any monomorphic call site; megamorphic call sites, which I would expect were rare, would have to do a hash lookup but not full operator resolution. By the way, did you say "mutual-asymmetric multimethod" :-)? > Function.defineOperator in the proposal binds both "this+" and "+this". I > agree these should not be plain old properties. But then why spec them as > named internal properties of any kind? > > Suppose we had a generic function "+" (syntax TBD) to which methods > could be added for particular non-conflicting pairs of operand types. Then > the lookup would be for two types A and B, but this can be optimized under > the hood. See, e.g., Methods live on objects and their prototypes. Operators should too. Using a special internal property rather than plain old properties is fine by me but they should be directly associated with the objects involved. I'd argue why that is so important but I'd like to be sure I understand what you're proposing as an alternative. As I understand it you would associate the operators with the constructor functions similar to python's five minute multimethods. Is that correct? _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
