[ruby-core:55363] [ruby-trunk - Bug #8072] Method#arity for keyword arguments

Issue #8072 has been updated by boris_stitnicky (Boris Stitnicky).


+1

Ruby has outgrown #arity. Today, plain #arity should only return positive value, when
the function has only compulsory ordered arguments. If there are any other arguments
(optional ordered arguments, named arguments, splat-collected arguments...), #arity
should return a negative value, meaning "Sorry, I give up, the negative integer I am
returning to you does not convey full information on this function's arguments."

However, I propose to make #arity work with one argument, and with terminology used
int the return values of #parameters method:

    f = -> a, b, c=1, d=2, *e, f: 3, g: 4, **h {}
    f.parameters
    #=> [[:req, :a], [:req, :b], [:opt, :c], [:opt, :d], [:rest, :e], [:key, :f], [:key, :g], [:keyrest, :h]]
    f.arity #=> -3
    f.arity( :req ) #=> 2
    f.arity( :opt ) #=> 2
    f.arity( :rest ) #=> 1
    f.arity( :key ) #=> 2
    f.arity( :keyrest ) #=> 1

    g = -> req, **named_arguments {}
    g.arity #=> -2
    g.arity( :req ) #=> 1
    g.arity( :opt ) #=> 0
    g.arity( :rest ) #=> 0
    g.arity( :key ) #=> 0
    g.arity( :keyrest ) #=> 1

----------------------------------------
Bug #8072: Method#arity for keyword arguments
https://bugs.ruby-lang.org/issues/8072#change-39782

Author: marcandre (Marc-Andre Lafortune)
Status: Open
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: current: 2.1.0
ruby -v: r39608
Backport: 


I would expect the following two methods to have the same arity:

    def old_way(req, options = {}); end
    def new_way(req, **options); end

    method(:new_way).arity # => 1, should be -2


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