From: James Coglan <jcoglan@...>
Date: 2009-07-08T17:54:28+09:00
Subject: Re: Symbol#to_proc with arguments

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2009/7/8 Max Williams <toastkid.williams@gmail.com>

> hey folks
>
> I've often wondered if i can use Symbol#to_proc with arguments - reading
> Dave Thomas's explanation on this page
> http://pragdave.pragprog.com/pragdave/2005/11/symbolto_proc.html it
> looks like i would be able to do this:
>
> >> array = %w(apple banana peach plum pear)
> => ["apple", "banana", "peach", "plum", "pear"]
> >> array.collect(&:split, 'l')
> SyntaxError: compile error
> (irb):12: syntax error, unexpected ',', expecting ')'
> array.collect(&:split, 'l')
>                      ^
> (irb):12: syntax error, unexpected ')', expecting $end
>  from (irb):12
>
> But it fails as you can see.  Trying to fully grasp what's going on with
> Symbol#to_proc makes my head hurt a little bit (it is only 9.16am here)
> and i'm clearly not getting it.  Can anyone explain?



The block argument (prefixed with '&') must be the last argument in the list
when calling a method, so passing 'l' in your example is not valid syntax.
You could rewrite Symbol#to_proc to take arguments, and call #to_proc
explicitly when calling #collect.

class Symbol
  def to_proc(*args)
    lambda { |o| o.__send__(self, *args) }
  end
end

%w[apple banana peach plum pear].collect &:split.to_proc('l')
#=> [["app", "e"], ["banana"], ["peach"], ["p", "um"], ["pear"]]

--
James Coglan
http://jcoglan.com

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