problem with metaprogramming

[Omer Katz]

Hi,

I'm bored and I'm trying to make a java-like 'interface' on c++. If I'll finish it I'll submit it to Loki :P

Now for some reason it gives me errors.

Here is the code:

#include <iostream>

#include <loki/Sequence.h>

#include <loki/Typelist.h>

using namespace std;

using namespace Loki;

using namespace Loki::TL;

template <typename Func, int Scope>

class FunctionTraits

{

public:

            enum { FuncScope = -1 };

};

template <typename Func>

class FunctionTraits<Func, 1>

{

protected:

            typedef Func FuncType;

public:

            enum { FuncScope = 1 };

};

template <typename Func>

class FunctionTraits<Func, 2>

{

public:

            typedef Func FuncType;

            enum { FuncScope = 2 };

};

template <class TL>

class interface;

template <typename Func1>

class interface<Seq<Func1> > : public Func1

{

public:

            typedef Func1 F1;

};

template <typename Func1, typename Func2>

class interface<Seq<Func1, Func2> > : public Func1, Func2

{

public:

            typedef Func1 F1;

            typedef Func2 F2;

};

template <typename Func1, typename Func2, typename Func3>

class interface<Seq<Func1, Func2, Func3> > : public Func1, Func2, Func3

{

public:

            typedef Func1 F1;

            typedef Func2 F2;

            typedef Func3 F3;

};

template <typename Func1, typename Func2, typename Func3, typename Func4>

class interface<Seq<Func1, Func2, Func3, Func4> > : public Func1, Func2, Func3, Func4

{

public:

            typedef Func1 F1;

            typedef Func2 F2;

            typedef Func3 F3;

            typedef Func4 F4;

};

template <typename Func1, typename Func2, typename Func3, typename Func4, typename Func5>

class interface<Seq<Func1, Func2, Func3, Func4, Func5> > : public Func1, Func2, Func3, Func4, Func5

{

public:

            typedef Func1 F1;

            typedef Func2 F2;

            typedef Func3 F3;

            typedef Func4 F4;

            typedef Func5 F5;

};

class TestFunc

{

public:

            void operator() (int);

};

class TestFunc1

{

public:

            int operator() ();

};

class InterfaceTest

{

            typedef interface<FunctionTraits<TestFunc, 2>, FunctionTraits<TestFunc1, 2> > myInterface; // ERROR HERE

public:

            InterfaceTest() { }

};

int main()

{

            cin.get();

  return 0;

   

}

main.cpp:95: error: wrong number of template arguments (2, should be 1)

main.cpp:34: error: provided for `template<class TL> struct interface'

main.cpp:95: error: ISO C++ forbids declaration of `myInterface' with no type

But let's say I use only one function in the interface.

Now InterfaceTest looks like this:

class InterfaceTest

{

            typedef interface<FunctionTraits<TestFunc, 2> > myInterface;

public:

            InterfaceTest() { myInterface::F1::FuncType()(); }

};

It generates those errors:

main.cpp: In constructor `InterfaceTest::InterfaceTest()':

main.cpp:97: error: `struct interface<FunctionTraits<TestFunc, 2> >::F1' has not been declared

main.cpp:97: error: `FuncType' undeclared (first use this function)

main.cpp:97: error: (Each undeclared identifier is reported only once for each function it appears in.)

Do you have any idea why?

Omer.

[Peter Kuemmel]

You've defined the interface template with only one parameter:

template <class TL>
class interface;

but at the error line there are two parameters.

[Omer Katz]

But when you guys implented Functor you did the same.
"    template <typename R, class TList,
        template <class, class> class ThreadingModel = LOKI_DEFAULT_THREADING_NO_OBJ_LEVEL>
    class FunctorImpl;"
"    template <typename R, typename P1, typename P2,
        template <class, class> class ThreadingModel>
    class FunctorImpl<R, Seq<P1, P2>, ThreadingModel>
        : public Private::FunctorImplBase<R, ThreadingModel>
    {
    public:
        typedef R ResultType;
        typedef typename TypeTraits<P1>::ParameterType Parm1;
        typedef typename TypeTraits<P2>::ParameterType Parm2;
        virtual R operator()(Parm1, Parm2) = 0;
    };"
In the second case there are more parameters and it still works.
What about the second error?

Omer.

[Peter Kuemmel]

No, in both cases there are three parameters.
This is the importand line:

class FunctorImpl<R, Seq<P1, P2>, ThreadingModel>

All the P1,P2... are necessary to construct the second parameter>:

1. R
2. TList=Seq<P1,P2> -> this is ONE Parameter
3. ThreadingModel

[Omer Katz]

But isn't that what I did?
"template <typename R, typename P1, typename P2, 
template <class, class> class ThreadingModel>
class FunctorImpl<R, Seq<P1, P2>, ThreadingModel> "

I used Seq too.

[Peter Kuemmel]

No, in the line with the error is no Seq used:

typedef interface<FunctionTraits<TestFunc, 2>, FunctionTraits<TestFunc1, 2> > myInterface; // ERROR HERE

Only when there a Seq is used it matches
1. with the general template definition of interface
2. it matches your specialization for Seq<P1,P2>

[Omer Katz]

Ok I get what was wrong.
Now why can't I access FuncType?

Omer.

[Omer Katz]

It works without FunctionTraits but I can't give up on it because I need the ScopeType to change the scope.
Btw what is the difference between Seq & MakeTypelist?

Omer

[Peter Kuemmel]

There are some specializations for Seq (Factory, Functor). And maybe there is also a compiler speed advantage for Seq because of less recursion.

[Peter Kuemmel]

And Functor also takes only three types (the last one has a default value):

Functor<void, Seq<int,int,int> >

[Peter Kuemmel]

So you must pass a Sequence:

typedef interface<Seq<FunctionTraits<TestFunc, 2>, FunctionTraits<TestFunc1,2> > > myInterface; // ERROR HERE