A Single Programmer's Blog

1 >> Party.find_by_email_address("sam@gamgee.net").if_not_nil do |party|
2 ?>   puts "Found Sam!"
3 >> end
4 => nil

 1 require File.dirname(__FILE__) + "/../test_helper"
 2 
 3 class SmalltalkTest < Test::Unit::TestCase
 4   setup do
 5     @block = Proc.new { true }
 6   end
 7 
 8   context "The nil object" do
 9     should "yield when calling #if_nil on it" do
10       assert nil.if_nil(&@block)
11     end
12 
13     should "not yield when calling #if_not_nil on it" do
14       deny nil.if_not_nil(&@block)
15     end
16   end
17 
18   context "A non nil object" do
19     should "not yield when calling #if_nil on it" do
20       deny "".if_nil(&@block)
21     end
22 
23     should "yield when calling #if_not_nil on it" do
24       assert "".if_not_nil(&@block)
25     end
26 
27     should "pass itself to #if_not_nil" do
28       obj = "abc"
29       assert_same obj, obj.if_not_nil {|o| o}
30     end
31   end
32 end

 1 # Copied and adapted from
 2 # http://recursive.ca/hutch/2007/11/22/a-little-unnecessary-smalltalk-envy/
 3 # Bob Huntchison
 4 class Object
 5   # yield self when it is non nil.
 6   def if_not_nil(&block)
 7     yield(self) if block
 8   end
 9 
10   # yield to the block if self is nil
11   def if_nil(&block)
12   end
13 end
14 
15 class NilClass
16   # yield self when it is non nil.
17   def if_not_nil(&block)
18   end
19 
20   # yield to the block if self is nil
21   def if_nil(&block)
22     yield if block
23   end
24 end