Re: Set#map! vs. map

On Tue, Jun 3, 2008 at 10:50 AM, David A. Black <[e-mail]> wrote:
> On Tue, 3 Jun 2008, Gary Wright wrote:
>>
>> If Array#map returns an array and Set#map returns a set, then shouldn't
>> Hash#map return a hash?
>
> Possibly it should, but not because of Array#map or Set#map. There's
> so much nuance to how all these Enumerable classes play out, in terms
> of their enumerability, that I don't think a universal rule is
> possible. I'm thinking of things like Range and File, as well as any
> number of classes that might be written mixing in Enumerable but that
> would not make sense as return values for a mapping.

Hash#map gets tricky all by itself, too - is it

def map(hash)
  a = {}
  hash.each {|k, v|
    f = yield [k,v]

    # option 1 :
    a[f[0]] = f[1]

    # option 2 :
    a[k] = f

    # option 3 :
    a[k] ||= []; a[k] << f

    # option 4:
    a[f[0]] ||= []; a[f[0]] << f[1]
  }
  return a
end