From 205b4c41b80b0b0ca995ea6a4dbd07757b609f8b Mon Sep 17 00:00:00 2001
From: Xavier Noria <fxn@hashref.com>
Date: Sun, 17 Jan 2010 00:33:24 +0100
Subject: AS guide: documents Class#reachable?

---
 .../source/active_support_core_extensions.textile  | 25 ++++++++++++++++++++++
 1 file changed, 25 insertions(+)

(limited to 'railties/guides/source/active_support_core_extensions.textile')

diff --git a/railties/guides/source/active_support_core_extensions.textile b/railties/guides/source/active_support_core_extensions.textile
index c911cb9c9f..a0b29dc30b 100644
--- a/railties/guides/source/active_support_core_extensions.textile
+++ b/railties/guides/source/active_support_core_extensions.textile
@@ -703,6 +703,31 @@ See also +Object#remove_subclasses_of+ in "Extensions to All Objects FIX THIS LI
 
 NOTE: Defined in +active_support/core_ext/class/removal.rb+.
 
+h4. Reachable Classes
+
+By definition a class is reachable if its name constantized is defined, and the corresponding constant evaluates to +self+:
+
+<ruby>
+class C; end
+C.reachable? # => true
+
+phantom = Object.send(:remove_const, :C)
+
+# The class object is orphan now but it still has a name.
+phantom.name # => "C"
+
+# Class name no longer available as a constant.
+phantom.reachable? # => nil
+
+# Let's define a class named "C" again.
+class C; end
+
+# Class name available as a constant, but different class object.
+phantom.reachable? # => false
+</ruby>
+
+NOTE: Defined in +active_support/core_ext/class/removal.rb+.
+
 h3. Extensions to +String+
 
 h4. +squish+
-- 
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