Re: [Swig-user] Swig and C++ singleton

[Cedric D. <ced...@in...>]

I am sorry, there are some typos in reported Swig messages.
One should read:

Error: Template 'Singleton' undefined.
Warning 401: Nothing known about base class 'Singleton< Foo >'. Ignored.
Warning 401: Maybe you forgot to instantiate 'Singleton< Foo >' using %template.

------- Simpler question -------------

How do you handle a nested definition like this?

template < class T > class Base {};
class Derived : public Base < Derived > {};

Best,

Cédric


----- Mail original -----
> De: "Cedric Doucet" <ced...@in...>
> À: "William S Fulton" <ws...@fu...>
> Cc: swi...@li...
> Envoyé: Mardi 17 Juin 2014 21:14:33
> Objet: Re: [Swig-user] Swig and C++ singleton
> 
> 
> 
> Thank you very much for your answer William.
> 
> Unfortunately, it does not work with
> 
> #include "singleton.hpp"
> %template(SingletonFoo) Singleton<Foo>;
> #include "foo.hpp"
> 
> I get the following messages:
> 
> Error: Template 'Singleton' undefined.
> Warning 401: Nothing known about base class 'Singleton< FelisceParam >'.
> Ignored.
> Warning 401: Maybe you forgot to instantiate 'Singleton< FelisceParam >'
> using %template.
> 
> I wonder if the problem comes from the fact that Foo inherits from
> Singleton<Foo> which should know Foo to be instantiated.
> 
> Thank you very much for your help!
> 
> 
> 
> 
> ----- Mail original -----
> > De: "William S Fulton" <ws...@fu...>
> > À: "Cedric Doucet" <ced...@in...>
> > Cc: swi...@li...
> > Envoyé: Mardi 17 Juin 2014 20:26:04
> > Objet: Re: [Swig-user] Swig and C++ singleton
> > 
> > On 16/06/14 16:11, Cedric Doucet wrote:
> > > Hello,
> > >
> > > I am trying to use Swig to use a C++ implementation of singleton pattern
> > > in Python but I do not manage to do it.
> > > I get these messages:
> > >      Warning 401: Base class 'Singleton< Foo >' undefined.
> > >      Warning 401: 'Singleton< Foo >' must be defined before it is used
> > > as a base class.
> > >
> > > My singleton class is defined by the following header file:
> > > ----------------------------------------------------------------------------
> > > singleton.hpp
> > > ----------------------------------------------------------------------------
> > > template<class T> class Singleton {
> > >    static T & instance()
> > >    { if ( !m_instance ) m_instance = new T(); return *m_instance; }
> > > protected:
> > >    Singleton(){}
> > >    ~Singleton(){}
> > > private:
> > >    Singleton(Singleton const &);
> > >    Singleton & operator=(Singleton const &);
> > > private:
> > >    static T * m_instance = NULL;
> > > };
> > > ----------------------------------------------------------------------------
> > >
> > > As usual, a singleton cannot be instantiated but the static method
> > > instance() returns the unique instance of the singleton after creating
> > > this instance if necessary.
> > > To make a singleton of type Foo, one may define Foo class like this:
> > > --------------------------------------------------------------------------------
> > > foo.hpp
> > > --------------------------------------------------------------------------------
> > > #include "singleton.hpp"
> > > class Foo : public Singleton<Foo>
> > > {
> > >      friend class Singleton<Foo>;
> > > public:
> > >      void my_method()
> > >      { /* implementation */ }
> > > private:
> > >    Foo(){};
> > >    ~Foo(){};
> > >    Foo(const Foo &);
> > >    Foo & operator=(Foo const &);
> > > };
> > > --------------------------------------------------------------------------------
> > >
> > > In practice, on uses Foo class by getting the unique instance of it and
> > > calling any member method, such as my_method, from it:
> > > -------------------------------------------------------------
> > > main.cpp
> > > -------------------------------------------------------------
> > > #include <cstdlib>
> > > #include "foo.hpp"
> > > int main()
> > > {
> > >      Foo::instance().my_method();
> > >      return EXIT_SUCCESS;
> > > }
> > >
> > > To create an interface with Swig, I have a file foo.i which contains the
> > > following lines:
> > >
> > > --------------------------------------------------------------
> > > foo.i
> > > --------------------------------------------------------------
> > > #include "singleton.hpp"
> > Move the %template below to here. It will then be instantiated in the
> > type system before it is used as a base in foo.hpp.
> > 
> > > #include "foo.hpp"
> > >
> > > %include "singleton.hpp"
> > > %include "foo.hpp"
> > >
> > > %template(SingletonFoo) Singleton<Foo>;
> > > --------------------------------------------------------------
> > >
> > 
> > William
> > 
> 
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