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Add a compatibility note about clang not implicitly converting between objc_object* and id (and SEL, Class). 

llvm-svn: 113761
This commit is contained in:
Argyrios Kyrtzidis 2010-09-13 17:48:07 +00:00
parent 2716b9ae54
commit cebc0f006f
1 changed files with 22 additions and 0 deletions
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clang/www/compatibility.html
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@ -40,6 +40,7 @@
<ul>
<li><a href="#super-cast">Cast of super</a></li>
<li><a href="#sizeof-interface">Size of interfaces</a></li>
<li><a href="#objc_objs-cast">Internal Objective-C types</a></li>
</ul>
</li>
<li><a href="#c++">C++ compatibility</a>
@ -233,6 +234,27 @@ this problem, use the Objective-C runtime API function
class_getInstanceSize([NSArray class])
</pre>
<!-- ======================================================================= -->
<h3 id="objc_objs-cast">Internal Objective-C types</h3>
<!-- ======================================================================= -->
<p>GCC allows using pointers to internal Objective-C objects, <tt>struct objc_object*</tt>,
<tt>struct objc_selector*</tt>, and <tt>struct objc_class*</tt> in place of the types
<tt>id</tt>, <tt>SEL</tt>, and <tt>Class</tt> respectively. Clang treats the
internal Objective-C structures as implementation detail and won't do implicit conversions:
<pre>
t.mm:11:2: error: no matching function for call to 'f'
f((struct objc_object *)p);
^
t.mm:5:6: note: candidate function not viable: no known conversion from 'struct objc_object *' to 'id' for 1st argument
void f(id x);
^
</pre>
<p>Code should use types <tt>id</tt>, <tt>SEL</tt>, and <tt>Class</tt>
instead of the internal types.</p>
<!-- ======================================================================= -->
<h2 id="c++">C++ compatibility</h3>
<!-- ======================================================================= -->