From: Jacob Fugal <lukfugl@...>
Date: 2005-08-06T01:39:54+09:00
Subject: Re: Yet Another useless Ruby 2 Idea

On 8/5/05, Daniel Brockman <daniel@brockman.se> wrote:
> > items.cool_method_name {|item| item*2 if item > 2}
> >
> > is quite doable in ruby
> 
> Except you can't collect nil values that way.

With that syntax, no. This would be a great place for multiple block
arguments though:

  module Enumerable
    def filter_and_map( &filter, &map )
      result = []
      self.each { |el| result << map[el] if filter[el] }
      return result
    end
  end
  
  [ 1, 2, 3, 4 ].filter_and_map { |i| i % 2 == 0 } { |i| i ** 2 }
  # => [ 4, 16 ]

Currently, this would have to written (the change to the method
implementation follows easily)

  [ 1, 2, 3, 4 ].filter_and_map( lambda{ |i| ... }, lambda{ |i| ... } )

Although, once we have named parameters and have settled on a syntax
for lambdas, it wouldn't be so bad:

  [ 1, 2, 3, 4 ].filter_and_map(
    filter: { |i| ... },
    map: { |i| ... },
  )

I'm with many of the other posters in this thread, however, and find
the list comprehension syntax even better[1]. Oh, well.

Jacob Fugal

[1] I think that ary.select{ |i| ... }.map{ |i| ... } may be even more
readable than the list comprehension, but it suffers performance due
to two passes through each of the accepted elements.