[cfe-commits] r152543 - /cfe/trunk/docs/LanguageExtensions.html

Douglas Gregor dgregor at apple.com
Sun Mar 11 10:21:03 PDT 2012

Author: dgregor
Date: Sun Mar 11 12:21:03 2012
New Revision: 152543

URL: http://llvm.org/viewvc/llvm-project?rev=152543&view=rev
Document the weak-linking behavior of the availability attribute


Modified: cfe/trunk/docs/LanguageExtensions.html
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/LanguageExtensions.html?rev=152543&r1=152542&r2=152543&view=diff
--- cfe/trunk/docs/LanguageExtensions.html (original)
+++ cfe/trunk/docs/LanguageExtensions.html Sun Mar 11 12:21:03 2012
@@ -665,6 +665,12 @@
   <dd>Apple's Mac OS X operating system. The minimum deployment target is specified by the <code>-mmacosx-version-min=<i>version</i></code> command-line argument.</dd>
+<p>A declaration can be used even when deploying back to a platform
+version prior to when the declaration was introduced. When this
+happens, the declaration is <a
+ href="https://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html">weakly
+linked</a>, as if the <code>weak_import</code> attribute were added to the declaration. A weakly-linked declaration may or may not be present a run-time, and a program can determine whether the declaration is present by checking whether the address of that declaration is non-NULL.</p>
 <!-- ======================================================================= -->
 <h2 id="checking_language_features">Checks for Standard Language Features</h2>
 <!-- ======================================================================= -->

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