On Sun Mar 08 07:02:33 2015, sml...@gmail.com wrote: > In current Rakudo, the 'is cached' trait for routines compares > incoming argument lists by their .gist representation. This was > probably done as a temporary work-around, and is not a satisfactory > solution because: > > * .gist elides information (e.g. cutting off lists/arrays after the > first few elements), thus causing false positives. > > * .gist is explicitly meant as a summary for human consumption, and > not for hashing/comparing objects. > > IRC discussion of the problem: > > masak: 'is cached' does some "snapshotting" of the incoming maybe- > reference > value, and it's that thing that's being eqv-compared with > what's in > the cache. (though right now it's being .gist-compared, which > may or > may not be goodenuf) > smls: well, seeing how gist truncates lists/arrays, it seems a > little unsafe > masak: yes, that's a *bug* > masak: actually, knowing that, using .gist in the first place is > *wrong*, > because the story for .gist is "string summary for > human/screen > consumption", not "exact eqv-like value for things like > hashing" > > IRC discussion about what a proper solution might look like: > > TimToady: I think each immutable type should have a hash function of > some > sort, and mutable types a way to snapshot to eqv semantics > masak: that sounds good so far, but I think we need more than > that. > TimToady: well, and a well-defined stragegy for combining hashes > masak: also, some things (like filehandles) probably don't have a > good > immutable/eqv representation. > TimToady: for filehandles and VAR($x) hashing the WHICH is probably > as good > as we can do > masak: right. that has to be an allowable fallback.
Since there was no obvious solution in sight, and there were other issues with "is cached", we've decided to defer this functionality to a future Perl 6 language version. So, removing it from the xmas list.
