From: Marc-Andre Lafortune <redmine@...>
Date: 2009-10-13T11:40:44+09:00
Subject: [ruby-core:26067] [Feature #1697] Object#<=>

Issue #1697 has been updated by Marc-Andre Lafortune.


I would modify slightly Nobu's patch to return 0 if the two compared objects are one and the same. I also think it is probably a better choice to return nil instead of raising an error.

With this patch in, running 'make test' doesn't generate any error. 'make test-all' generates two, on for rake because Rake::FileList has a weak way to find which methods are proper to Array, and another error because of Delegator, which doesn't inherit from BasicObject (see issue 1333) and doesn't list :<=> in its list of methods to undefine. So both of these are trivially fixed.

Although I really would like an implementation of a good double dispatch scheme, I'll leave that discussion for another time.


diff --git a/object.c b/object.c
index e81007b..fdf1ee6 100644
--- a/object.c
+++ b/object.c
@@ -1115,13 +1115,23 @@ rb_obj_not_match(VALUE obj1, VALUE obj2)
     return RTEST(result) ? Qfalse : Qtrue;
 }
 
-/* :nodoc: */
+/*
+ *  call-seq:
+ *     obj <=> other       => -1, 0, 1 or nil
+ *
+ *  Comparison---Returns -1 if <i>obj</i> is smaller than <i>other</i>,
+ *  0 if <i>obj</i> is the same as <i>other</i>, and +1 if <i>obj</i> is
+ *  greater than <i>other</i>. Returns <code>nil</code> if <i>obj</i>
+ *  can not be compared with <i>other</i>.
+ *  Typically, this method is overridden in descendent
+ *  classes to provide class-specific meaning.
+ */
+
 static VALUE
 rb_obj_cmp(VALUE obj, VALUE arg)
 {
-    if (!rb_respond_to(arg, id_cmp)) {
-       rb_notimplement();
-    }
+    if (obj == arg)
+       return INT2FIX(0);
     return Qnil;
 }

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http://redmine.ruby-lang.org/issues/show/1697

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