# New Ticket Created by Sam S.
# Please include the string: [perl #124016]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org/Ticket/Display.html?id=124016 >
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.
