Author: dgregor
Date: Tue Jan 15 19:12:31 2013
New Revision: 172587
URL: http://llvm.org/viewvc/llvm-project?rev=172587&view=rev
Log:
Document the redeclaration and overriding restrictions on the
availability attribute.
Modified:
cfe/trunk/docs/LanguageExtensions.rst
Modified: cfe/trunk/docs/LanguageExtensions.rst
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/LanguageExtensions.rst?rev=172587&r1=172586&r2=172587&view=diff
==============================================================================
--- cfe/trunk/docs/LanguageExtensions.rst (original)
+++ cfe/trunk/docs/LanguageExtensions.rst Tue Jan 15 19:12:31 2013
@@ -439,7 +439,7 @@
Finally, if Clang is instructed to compile code for Mac OS X 10.7, the call
fails because ``f()`` is no longer available.
-The availablility attribute is a comma-separated list starting with the
+The availability attribute is a comma-separated list starting with the
platform name and then including clauses specifying important milestones in the
declaration's lifetime (in any order) along with additional information. Those
clauses can be:
@@ -488,6 +488,33 @@
can determine whether the declaration is present by checking whether the
address of that declaration is non-NULL.
+If there a multiple declarations of the same entity, the availability
+attributes must either match on a per-platform basis or later
+declarations must not have availability attributes for that
+platform. For example:
+
+.. code-block:: c
+
+ void g(void) __attribute__((availability(macosx,introduced=10.4)));
+ void g(void) __attribute__((availability(macosx,introduced=10.4))); // okay,
matches
+ void g(void) __attribute__((availability(ios,introduced=4.0))); // okay,
adds a new platform
+ void g(void); // okay, inherits both macosx and ios availability from above.
+ void g(void) __attribute__((availability(macosx,introduced=10.5))); //
error: mismatch
+
+When one method overrides another, the overriding method can be more widely
available than the overridden method, e.g.,:
+
+.. code-block:: objc
+
+ @interface A
+ - (id)method __attribute__((availability(macosx,introduced=10.4)));
+ - (id)method2 __attribute__((availability(macosx,introduced=10.4)));
+ @end
+
+ @interface B : A
+ - (id)method __attribute__((availability(macosx,introduced=10.3))); // okay:
method moved into base class later
+ - (id)method __attribute__((availability(macosx,introduced=10.5))); //
error: this method was available via the base class in 10.4
+ @end
+
Checks for Standard Language Features
=====================================
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