From: Robert Klemme <shortcutter@...>
Date: 2013-03-26T06:58:30+09:00
Subject: Re: Confusion with Array#map

On Mon, Mar 25, 2013 at 7:41 PM, tamouse mailing lists
<tamouse.lists@gmail.com> wrote:
> On Mon, Mar 25, 2013 at 1:37 PM, Love U Ruby <lists@ruby-forum.com> wrote:

>> How `proc` object is getting called by `call` to produce the output? Who
>> is calling that?
>
> The operator "&" is the block operator, which is turning the symbol
> :capitalize which refers to the method capitalize in that context.
> Since at that point, map is sending in strings, it says to call the
> capitalize method on that string.
> https://en.wikibooks.org/wiki/Ruby_Programming/Syntax/Method_Calls#The_Ampersand_Operator

The crucial bit here is that Symbol#to_proc exists.  Actually anything
can be used in that way:

irb(main):001:0> o = Object.new
=> #<Object:0x802bdf10>
irb(main):002:0> def o.to_proc; lambda {|x| "<#{x.inspect}>"}
irb(main):003:1> end
=> nil
irb(main):004:0> (1..5).map(&o)
=> ["<1>", "<2>", "<3>", "<4>", "<5>"]

Cheers

robert


-- 
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