From 79fabe094a39c390205c778d4ccb32c9470c7a1a Mon Sep 17 00:00:00 2001
From: Bryan Larsen <bryan@larsen.st>
Date: Wed, 18 Nov 2009 09:28:22 -0500
Subject: [PATCH] [#537 state:resolved]

This changes the behaviour of the `._?.` "dot".  It now returns 'nil'
rather than calling the trailing function more often.
---
 hobosupport/lib/hobo_support/methodcall.rb |   27 +++++++++++++++++++++++++--
 hobosupport/test/hobosupport.rdoctest      |   18 +++++++++++++++++-
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/hobosupport/lib/hobo_support/methodcall.rb b/hobosupport/lib/hobo_support/methodcall.rb
index 85b688a..f3028e0 100644
--- a/hobosupport/lib/hobo_support/methodcall.rb
+++ b/hobosupport/lib/hobo_support/methodcall.rb
@@ -56,9 +56,32 @@ end
 class SafeNil
   include Singleton
 
+  DONT_REDEFINE_METHODS = "__id__", "__send__"
+
+  NIL_RESPONSE_METHODS = ["to_s", "to_json", "to_yaml", "__id__", "__is_a__", "__metaclass__", "__send__"]
+
+  (NIL_RESPONSE_METHODS - DONT_REDEFINE_METHODS).each do |method|
+    # can't use define_method with a block
+    eval "
+      def #{method}(*args, &b)
+        nil.send(:#{method}, *args, &b)
+      end"
+  end
+
+  (instance_methods - NIL_RESPONSE_METHODS - DONT_REDEFINE_METHODS).each do |method|
+    # can't use define_method with a block
+    eval "
+      def #{method}(*args, &b)
+        nil
+      end"
+  end
+
+  def to_s
+    ""
+  end  
+
   def method_missing(method, *args, &b)
-    return nil unless nil.respond_to? method
-    nil.send(method, *args, &b) rescue nil
+    return nil
   end
 end
 
diff --git a/hobosupport/test/hobosupport.rdoctest b/hobosupport/test/hobosupport.rdoctest
index 66b22db..9e0241b 100644
--- a/hobosupport/test/hobosupport.rdoctest
+++ b/hobosupport/test/hobosupport.rdoctest
@@ -34,15 +34,21 @@ Like `is_a?` but multiple types to be checked in one go
 
 ## Method call extensions
 
+We have the "." operator to call methods on objects. These extensions introduce two "special dots". 
+
 ### `Object#_?`
 
-We have the "." operator to call methods on objects. These extensions introduce two "special dots". "`._?.`" only calls the method if the receiver is not `nil`.
+"`._?.`" only calls the method if the receiver is not `nil`.  Otherwise it returns nil.
 
     >> "foo"._?.length
     => 3
     >> nil._?.length
     => nil
 
+`to_s`, `to_yaml` and `to_json` and a few system functions that start with an underscore are the only exceptions -- they call their corresponding functions on nil.
+
+    >> nil._?.to_s
+    => ""
 
 ### `Object#try`
 
@@ -53,4 +59,14 @@ We have the "." operator to call methods on objects. These extensions introduce
     >> :foo.try.length
     => nil
 
+### What's the difference?
 
+`_?` is generally used when nil is an expected response.  `try` is
+generally used when interfaces may be different.  For instance, you
+may use `try` to call a Rails 2.3 function that doesn't exist on Rails
+2.2.  nil responds to some functions that may surprise you.
+
+    >> nil.try.to_i
+    => 0
+    >> nil._?.to_i
+    => nil
-- 
1.6.3.3