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More tweaks to the compatibility page.

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llvm-svn: 124792
This commit is contained in:
John McCall 2011-02-03 11:29:18 +00:00
parent 93adb039b5
commit 2bd04c3114
1 changed files with 24 additions and 22 deletions
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46
clang/www/compatibility.html
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@ -65,7 +65,7 @@
<li><a href="#implicit-downcasts">Implicit downcasts</a></li>
</ul>
<ul>
<li><a href="#Use of class as method name">Use of class as method name</a></li>
<li><a href="#class-as-property-name">Using <code>class</code> as a property name</a></li>
</ul>
</li>
</ul>
@ -418,8 +418,8 @@ compatibility with GNU C and C99 programs:</p>
<ul>
<li>The element type of a variable length array must be a POD
("plain old data") type, which means that it cannot have any
user-declared constructors or destructors, base classes, or any
members if non-POD type. All C types are POD types.</li>
user-declared constructors or destructors, any base classes, or any
members of non-POD type. All C types are POD types.</li>
<li>Variable length arrays cannot be used as the type of a non-type
template parameter.</li> </ul>
@ -428,12 +428,9 @@ template parameter.</li> </ul>
<ol>
<li>replace the variable length array with a fixed-size array if you can
determine a
reasonable upper bound at compile time; sometimes this is as
determine a reasonable upper bound at compile time; sometimes this is as
simple as changing <tt>int size = ...;</tt> to <tt>const int size
= ...;</tt> (if the definition of <tt>size</tt> is a compile-time
integral constant);</li>
<li>use <tt>std::string</tt> instead of a <tt>char []</tt>;</li>
= ...;</tt> (if the initializer is a compile-time constant);</li>
<li>use <tt>std::vector</tt> or some other suitable container type;
or</li>
<li>allocate the array on the heap instead using <tt>new Type[]</tt> -
@ -762,18 +759,18 @@ void f(int a, int a);
<!-- ======================================================================= -->
<p>Due to a bug in its implementation, GCC allows implicit downcasts
(from base class to a derived class) when calling functions. Such code is
inherently unsafe, since the object might not actually be an instance
of the derived class, and is rejected by Clang. For example, given
this code:</p>
of Objective-C pointers (from a base class to a derived class) when
calling functions. Such code is inherently unsafe, since the object
might not actually be an instance of the derived class, and is
rejected by Clang. For example, given this code:</p>
<pre>
@interface Base @end
@interface Derived : Base @end
void f(Derived *);
void g(Base *base) {
f(base);
void f(Derived *p);
void g(Base *p) {
f(p);
}
</pre>
@ -781,11 +778,11 @@ void g(Base *base) {
<pre>
downcast.mm:6:3: error: no matching function for call to 'f'
f(base);
f(p);
^
downcast.mm:4:6: note: candidate function not viable: cannot convert from
superclass 'Base *' to subclass 'Derived *' for 1st argument
void f(Derived *);
void f(Derived *p);
^
</pre>
@ -798,13 +795,17 @@ explicit cast:</p>
</pre>
<!-- ======================================================================= -->
<h3 id="Use of class as method name">Use of class as method name</h3>
<h3 id="class-as-property-name">Using <code>class</code> as a property name</h3>
<!-- ======================================================================= -->
<p>Use of 'class' name to declare a method is allowed in objective-c++ mode to
be compatible with GCC. However, use of property dot syntax notation to call
this method is not allowed in clang++, as [I class] is a suitable syntax that
will work. So, this test will fail in clang++.
<p>In C and Objective-C, <code>class</code> is a normal identifier and
can be used to name fields, ivars, methods, and so on. In
C++, <code>class</code> is a keyword. For compatibility with existing
code, Clang permits <code>class</code> to be used as part of a method
selector in Objective-C++, but this does not extend to any other part
of the language. In particular, it is impossible to use property dot
syntax in Objective-C++ with the property name <code>class</code>, so
the following code will fail to parse:</p>
<pre>
@interface I {
@ -818,6 +819,7 @@ int cls;
@end
<pre>
<p>Use explicit message-send syntax instead, i.e. <code>[I class]</code>.</p>
</div>
</body>