[Qt-interest] Problems with template and function pointer

[Sean Harmer]

On Thursday 04 November 2010 14:16:01 mario wrote:
> 2010/11/4 Sean Harmer <sean.harmer at maps-technology.com>:
> > ( *this.*m_function )();
> 
> I tried...
> (this->*p)();
> //error: pointer to member type ‘void (ModuleTest::)()’ incompatible
> with object type ‘Module<ModuleTest>’

This is your clue. The following 2 options both work. Up to you which you go 
for or some variation on them:

#include <QDebug>

template <typename T> class Module
{
public:
    typedef void (T::*memberPtr)(  );
    typedef QMap<QString, memberPtr> ModuleFunctMap;

    Module(){ m_object = 0; }

    void caller( const QString& functName)  {
            if ( m_mFunctionMap.contains(functName)  ) {

                    memberPtr p = this->m_mFunctionMap[functName];

                    // Cannot simply use *this.*p as *this is not a class
                    // of type T

                    // Option 1
                    // No dangerous assumptions. We simply call the function
                    // on the object we have been given.
                    if ( m_object )
                        (*m_object.*p)();

                    // Option 2
                    // Makes assumption that we can cast this to a T*
                    T* obj = static_cast<T*>( this );
                    (*obj.*p)();
            }
    }


protected:
    T* m_object; // Only needed for option 1
    ModuleFunctMap  m_mFunctionMap;
};


class ModuleTest : public Module<ModuleTest>
{
public:
    ModuleTest(  ) {
        m_object = this; // Only needed for option 1
        m_mFunctionMap["randomFunctioName"] = &ModuleTest::functionToCall;
    }

    void functionToCall() {
        qDebug() << "YEAH!";
    }
};


int main(int argc, char *argv[])
{
    ModuleTest test;
    test.caller("randomFunctioName");
    return 0;
}

HTH,

Sean