Feature #8053
closed
Make coercion if #=== operator doesn't know what to do
Description
Related to http://bugs.ruby-lang.org/issues/7604
It'd be fine if === will do coerce when it doesn't know what to do. In ticket above I gave use-case for case-statement which needs that any ruby object could be coerced to a "pattern".
For example
case arr.end_with?
when ['several', 'words'] then puts 'arr have last two elements: several, words'
when ['word'] then puts 'arr have last element: word'
else puts 'cannot understand'
end
It'd be possible if Array#===(predicate) will simply use usual coerce call: predicate.coerce(arr) -- Predicate#coerce is a good point to understand behavior of such matching.
Another example:
class FalseYielder
def ===(other)
false
end
end
class MyString
def initalize(string); @string = string; end
attr_reader :string
def coerce(other)
if other.is_a? Regexp
[other, self.string]
else
[FalseYielder.new, self]
end
end
end
case MyString.new('abcpatdef')
when /pat/ then 'it works'
end
Here we shouldn't monkeypatch Regexp class and it's good, we can make an error only in our own class MyString.
Updated by
Updated by matz (Yukihiro Matsumoto) almost 12 years ago
- Status changed from Assigned to Rejected
Objects except for numbers does not have coerce protocol. I am not sure how far OP wants to dig in.
Design and implement coerce protocol? Or special kind of coercion for case statement?
In that sense, this proposal is half-baked.
Re-submit if you come up with concrete behavior definition, e.g. what "doesn't know" mean.
Matz.
Updated by Anonymous almost 12 years ago
Sorry, Ilya, I already did some thinking, but didn't finish that flex-coerce yet.