<br><font size=2 color=#800080 face="sans-serif">> Chris Fairles"
<chris.fairles@gmail.com> on Fri, 20 Jul 2007 18:03:18 -0400</font>
<br><tt><font size=2>> How can you determine (compile-time) that a class
has a serialize function?<br>
> <br>
> struct foo {<br>
> template <typename Archive><br>
> void serialize (Archive &, const unsigned int);<br>
> };<br>
> <br>
> "&foo::serialize" isn't a type and I can't figure out
a way to make it<br>
> a type (besides a typedef in the class) and also a constant<br>
> expression.<br>
> <br>
> Tried to play around with this as well but theres no substitution<br>
> failure here and static functions can't be constant expressions<br>
> (commonnnn c++0x!!)<br>
> <br>
> struct serialize {<br>
> template <typename T><br>
> static void value(T const&) { void(T::*f)(archive::xml_oarchive
&,<br>
> const unsigned int) = &T::template serialize<archive::xml_oarchive>;<br>
> (void)f; }<br>
> };<br>
> <br>
> Basically, in the code below I want to see "GoodGood" printed
out and<br>
> the only thing I can change is Q.<br>
> <br>
> struct A{<br>
> void f(int,int){}<br>
> };<br>
> struct B{};<br>
> <br>
> template <class T,class F=void><br>
> struct Q{enum{value=false};};<br>
> <br>
> template<class T> struct Q<T,void(T::serialize)(int,int)>{enum{value=true};};<br>
> <br>
> int main(){<br>
> if(Q<A>::value) { cout << "Good";}<br>
> if(!Q<B>::value){ cout << "Good";}<br>
> }<br>
> <br>
> Help/hints/remotely possible?</font></tt>
<br>
<br><font size=2 face="sans-serif">You can try something like this.</font>
<br>
<br><font size=2 color=blue>#include</font><font size=2> </font><font size=2 color=#a11f12><iostream></font>
<br><font size=2 color=blue>#include</font><font size=2> </font><font size=2 color=#a11f12><iomanip></font>
<br>
<br><font size=2 color=blue>typedef</font><font size=2> </font><font size=2 color=blue>char</font><font size=2>
yes_type;</font>
<br>
<br><font size=2 color=blue>struct</font><font size=2> no_type</font>
<br><font size=2>{</font>
<br><font size=2> </font><font size=2 color=blue>char</font><font size=2>
padding[8];</font>
<br><font size=2>};</font>
<br>
<br><font size=2 color=blue>template</font><font size=2> <</font><font size=2 color=blue>class</font><font size=2>
T></font>
<br><font size=2 color=blue>struct</font><font size=2> HasSerializeMember</font>
<br><font size=2>{</font>
<br><font size=2> </font><font size=2 color=blue>typedef</font><font size=2>
</font><font size=2 color=blue>void</font><font size=2> (T::*SerializationFun)(</font><font size=2 color=blue>int</font><font size=2>
&, </font><font size=2 color=blue>unsigned</font><font size=2>);</font>
<br>
<br><font size=2> </font><font size=2 color=blue>template</font><font size=2>
<SerializationFun></font>
<br><font size=2> </font><font size=2 color=blue>struct</font><font size=2>
A {};</font>
<br>
<br><font size=2> </font><font size=2 color=blue>template</font><font size=2>
<</font><font size=2 color=blue>class</font><font size=2> Q></font>
<br><font size=2> </font><font size=2 color=blue>static</font><font size=2>
yes_type Test(A<&Q::serialize>*);</font>
<br>
<br><font size=2> </font><font size=2 color=blue>template</font><font size=2>
<</font><font size=2 color=blue>class</font><font size=2> Q></font>
<br><font size=2> </font><font size=2 color=blue>static</font><font size=2>
no_type Test(...);</font>
<br>
<br><font size=2> </font><font size=2 color=blue>static</font><font size=2>
</font><font size=2 color=blue>const</font><font size=2> </font><font size=2 color=blue>bool</font><font size=2>
value =</font>
<br><font size=2> </font><font size=2 color=blue>sizeof</font><font size=2>(Test<T>(0))
== </font><font size=2 color=blue>sizeof</font><font size=2>(yes_type);</font>
<br><font size=2>};</font>
<br>
<br><font size=2 color=blue>struct</font><font size=2> A</font>
<br><font size=2>{</font>
<br><font size=2> </font><font size=2 color=blue>template</font><font size=2>
<</font><font size=2 color=blue>class</font><font size=2> Stream></font>
<br><font size=2> </font><font size=2 color=blue>void</font><font size=2>
serialize(Stream & strm, </font><font size=2 color=blue>unsigned</font><font size=2>
version) {}</font>
<br><font size=2>};</font>
<br>
<br><font size=2 color=blue>struct</font><font size=2> B</font>
<br><font size=2>{</font>
<br><font size=2>};</font>
<br>
<br><font size=2 color=blue>struct</font><font size=2> C</font>
<br><font size=2>{</font>
<br><font size=2> </font><font size=2 color=blue>void</font><font size=2>
serialize() {}</font>
<br><font size=2>};</font>
<br>
<br><font size=2 color=blue>int</font><font size=2> main()</font>
<br><font size=2>{</font>
<br><font size=2> </font><font size=2 color=blue>using</font><font size=2>
</font><font size=2 color=blue>namespace</font><font size=2> std;</font>
<br><font size=2> cout</font>
<br><font size=2> << boolalpha</font>
<br><font size=2> << HasSerializeMember<A>::value
<< </font><font size=2 color=#a11f12>'\n'</font><font size=2> </font><font size=2 color=#008000>//
true</font>
<br><font size=2> << HasSerializeMember<B>::value
<< </font><font size=2 color=#a11f12>'\n'</font><font size=2> </font><font size=2 color=#008000>//
false</font>
<br><font size=2> << HasSerializeMember<C>::value
<< endl; </font><font size=2 color=#008000>// false</font>
<br><font size=2>}</font>
<br>
<br><font size=2 face="sans-serif">Regards,<br>
Roman Perepelitsa<br>
<br>
Deutsche Bank Moscow<br>
+7 (495) 660-74-08<br>
</font>
<br>
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