From: Benoit Daloze <eregontp@...>
Date: 2009-10-30T19:48:48+09:00
Subject: Re: Why (1..4).inject(&:+) works ?

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In fact, I knew about about the 1.8 implementations. I just forgot about it.
Thank to have cleared my ideas.

The current implementation looks like (of course it must be in C):

class Symbol
    def to_proc
        @to_proc ||= Proc.new { |*args| args.shift.send(self, *args) }
    end
end

2009/10/30 Rick DeNatale <rick.denatale@gmail.com>

> On Thu, Oct 29, 2009 at 2:14 PM, Benoit Daloze <eregontp@gmail.com> wrote:
> > Hi rubyists,
> >
> > I was just wondering why,
> >
> > (1..4).inject(&:+) #=> 10
> >
> > works ? (in Ruby 1.9.2)
> >
> > I understand easily these:
> >
> > (1..4).inject { |s, e| s + e } #=> 10
> > (1..4).inject(:+) #=> 10
> >
> > I suppose it's calling :+.to_proc #=> #<Proc:0x2f52d8>
> >
> > irb> def a(&b); b; end
> > irb> a(&:+)
> > => #<Proc:0x2f52d8>
> > irb> :+.to_proc
> > => #<Proc:0x2f52d8>
> >
> > irb> p = a(&:+)
> > => #<Proc:0x2f52d8>
> > irb> p.arity
> > => -1
> > irb> p.call(1,2)
> > => 3
> > irb> p.call(1)
> > ArgumentError: wrong number of arguments(0 for 1)
> >    ...
> > irb> p.call(1,2,3)
> > ArgumentError: wrong number of arguments(2 for 1)
> >   ...
> > irb> p.call
> > ArgumentError: no receiver given
> >
> > Well, that's strange: arity = -1, so normally only optional arguments.
> And
> > it expects 1 argument but want 2 ?
> > "no receiver given" : That means it knows it has a argument to act on
> like
> > a.+(b). How come ?
> > Would &:+ knows it need some object to act with "+"(o) ?
>
> irb(main):001:0> 1.send(:+)
> ArgumentError: wrong number of arguments(0 for 1)
>         from (irb):1:in `+'
>        from (irb):1
>        from /Users/rick/.rvm/ruby-1.9.1-p243/bin/irb:12:in `<main>'
> irb(main):002:0> 1.send(:+, 2)
> => 3
> irb(main):003:0> 1.send(:+, 2, 3)
> ArgumentError: wrong number of arguments(2 for 1)
>         from (irb):3:in `+'
>        from (irb):3
>        from /Users/rick/.rvm/ruby-1.9.1-p243/bin/irb:12:in `<main>'
>
>
> --
> Rick DeNatale
>
> Blog: http://talklikeaduck.denhaven2.com/
> Twitter: http://twitter.com/RickDeNatale
> WWR: http://www.workingwithrails.com/person/9021-rick-denatale
> LinkedIn: http://www.linkedin.com/in/rickdenatale
>
>

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