From: Josh Cheek <josh.cheek@...>
Date: 2010-04-14T14:45:41+09:00
Subject: Re: i don't know:&:empty?

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On Wed, Apr 14, 2010 at 12:18 AM, Pen Ttt <myocean135@yahoo.cn> wrote:

> there is one commade:
> '["ffgh"]78'.split(/\[|\]/).reject(&:empty?)
> i can get two character: "ffgh"  78
> but i don't know what is the meaning of :
> &:empty?
> 1\what is :
> 2\what is &:
> think you for advance.
> --
> Posted via http://www.ruby-forum.com/.
>
>
:empty? is a symbol, & converts it to a proc. This is the same as saying
'["ffgh"]78'.split(/\[|\]/).reject { |str| str.empty? }

It's purpose seems to be to remove the empty string from splitting on the
first character (that first bracket).

p '["ffgh"]78'.split(/\[|\]/)
p '["ffgh"]78'.split(/\[|\]/).reject { |str| str.empty? }
p '["ffgh"]78'.split(/\[|\]/).reject(&:empty?)




To better illustrate, lets implement something similar. Here is an example,
where we do the same thing with a String as you do with the Symbol. (It is a
hypothetical implementation, I don't know how Ruby actually has it
implemented.)


puts RUBY_VERSION # for me: 1.9.1

counts = %w(first second)
begin
  puts "#{counts.shift} time trying &'empty?'"
  p '["ffgh"]78'.split(/\[|\]/).reject(&'empty?')
rescue
  puts "rescued because String doesn't have a to_proc method"
  class String
    def to_proc
      lambda { |obj| obj.send self }
    end
  end
  puts "If this was successful, then you should see the same results for
&'empty?' as &:empty?"
  retry
end

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