From: Brian Mitchell <binary42@...>
Date: 2006-01-07T20:03:56+09:00
Subject: Re: Iterator Fu Failing Me

On 1/6/06, James Edward Gray II <james@grayproductions.net> wrote:
> I have a group of classes, all implementing a parse?() class method.
> Calling parse?(token) will return the constructed object, if it can
> be parsed by this class, or false otherwise.
>
> I want to run a bunch of tokens through these classes, grabbing the
> first fit.  For example:
>
>    elements = tokens.map do |token|
>      ClassA.parse?(token) or
>      ClassB.parse?(token) or
>      ClassC.parse?(token)
>    end
>
> That works.  Now can anyone give me a version of the middle section
> that doesn't require I call parse?() 50 times?  I want something
> close to:
>
>    elements = tokens.map do |token|
>      [ClassA, ClassB, ClassC].find { |kind| kind.parse?(token) }
>    end
>

How about:

elements = tokens.map do |token|
  [ClassA, ClassB, ClassC].inject(false) {|m, kind| m or kind.parse?(token)}
end

It isn't perfectly efficient but it is short.

Brian.