Re: [Boost-users] [Serialization] is_serializable trait?

From: Roman Perepelitsa (roman.perepelitsa_at_[hidden])
Date: 2007-07-23 02:27:16

> Chris Fairles" <chris.fairles_at_[hidden]> on Fri, 20 Jul 2007 18:03:18 
-0400
> How can you determine (compile-time) that a class has a serialize 
function?
> 
> struct foo {
> template <typename Archive>
> void serialize (Archive &, const unsigned int);
> };
> 
> "&foo::serialize" isn't a type and I can't figure out a way to make it
> a type (besides a typedef in the class) and also a constant
> expression.
> 
> Tried to play around with this as well but theres no substitution
> failure here and static functions can't be constant expressions
> (commonnnn c++0x!!)
> 
> struct serialize {
>     template <typename T>
>     static void value(T const&) { void(T::*f)(archive::xml_oarchive &,
> const unsigned int) = &T::template serialize<archive::xml_oarchive>;
> (void)f; }
> };
> 
> Basically, in the code below I want to see "GoodGood" printed out and
> the only thing I can change is Q.
> 
> struct A{
>   void f(int,int){}
> };
> struct B{};
> 
> template <class T,class F=void>
> struct Q{enum{value=false};};
> 
> template<class T> struct 
Q<T,void(T::serialize)(int,int)>{enum{value=true};};
> 
> int main(){
>   if(Q<A>::value) { cout << "Good";}
>   if(!Q<B>::value){ cout << "Good";}
> }
> 
> Help/hints/remotely possible?

You can try something like this.

#include <iostream>
#include <iomanip>

typedef char yes_type;

struct no_type
{
   char padding[8];
};

template <class T>
struct HasSerializeMember
{
    typedef void (T::*SerializationFun)(int &, unsigned);

    template <SerializationFun>
    struct A {};

    template <class Q>
    static yes_type Test(A<&Q::serialize>*);

    template <class Q>
    static no_type Test(...);

    static const bool value =
        sizeof(Test<T>(0)) == sizeof(yes_type);
};

struct A
{
    template <class Stream>
    void serialize(Stream & strm, unsigned version) {}
};

struct B
{
};

struct C
{
    void serialize() {}
};

int main()
{
    using namespace std;
    cout
        << boolalpha
        << HasSerializeMember<A>::value << '\n'  // true
        << HasSerializeMember<B>::value << '\n'  // false
        << HasSerializeMember<C>::value << endl; // false
}

Regards,
Roman Perepelitsa

Deutsche Bank Moscow
[phone]

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