lumiera_/research/try.cpp

/* try.cpp  -  for trying out some language features....
 *             scons will create the binary bin/try
 *
 */

// 8/07  - how to control NOBUG??
//         execute with   NOBUG_LOG='ttt:TRACE' bin/try
// 1/08  - working out a static initialisation problem for Visitor (Tag creation)
// 1/08  - check 64bit longs
// 4/08  - comparison operators on shared_ptr<Asset>
// 4/08  - conversions on the value_type used for boost::any
// 5/08  - how to guard a downcasting access, so it is compiled in only if the involved types are convertible
// 7/08  - combining partial specialisation and subclasses
// 10/8  - abusing the STL containers to hold noncopyable values
// 6/09  - investigating how to build a mixin template providing an operator bool()
// 12/9  - tracking down a strange "warning: type qualifiers ignored on function return type"
// 1/10  - can we determine at compile time the presence of a certain function (for duck-typing)?
// 4/10  - pretty printing STL containers with python enabled GDB?
// 1/11  - exploring numeric limits
// 1/11  - integer floor and wrap operation(s)
// 1/11  - how to fetch the path of the own executable -- at least under Linux?
// 10/11 - simple demo using a pointer and a struct
// 11/11 - using the boost random number generator(s)
// 12/11 - how to detect if string conversion is possible?
// 1/12  - is partial application of member functions possible?
// 5/14  - c++11 transition: detect empty function object
// 7/14  - c++11 transition: std hash function vs. boost hash
// 9/14  - variadic templates and perfect forwarding
// 11/14 - pointer to member functions and name mangling
// 8/15  - Segfault when loading into GDB (on Debian/Jessie 64bit
// 8/15  - generalising the Variant::Visitor
// 1/16  - generic to-string conversion for ostream
// 1/16  - build tuple from runtime-typed variant container
// 3/17  - generic function signature traits, including support for Lambdas
// 9/17  - manipulate variadic templates to treat varargs in several chunks
// 11/17 - metaprogramming to detect the presence of extension points
// 11/17 - detect generic lambda
// 12/17 - investigate SFINAE failure. Reason was indirect use while in template instantiation
// 03/18 - Dependency Injection / Singleton initialisation / double checked locking


/** @file try.cpp
 ** Rework of the template lib::Depend for singleton and service access.
 */

typedef unsigned int uint;

#include "lib/format-cout.hpp"
#include "lib/depend.hpp"
#include "lib/depend2.hpp"
#include "lib/meta/util.hpp"
//#include "lib/meta/util.hpp"
#include "lib/test/test-helper.hpp"
#include "lib/util.hpp"

#include <boost/noncopyable.hpp>
#include <functional>
#include <type_traits>
#include <memory>


#define SHOW_TYPE(_TY_) \
    cout << "typeof( " << STRINGIFY(_TY_) << " )= " << lib::meta::typeStr<_TY_>() <<endl;
#define SHOW_EXPR(_XX_) \
    cout << "Probe " << STRINGIFY(_XX_) << " ? = " << _XX_ <<endl;


namespace error = lumiera::error;

using lib::ClassLock;
using lib::meta::enable_if;


namespace {
  template<typename TAR, typename SEL =void>
  class InstanceHolder
    : boost::noncopyable
    {
      std::unique_ptr<TAR> instance_;
      
      
    public:
      TAR*
      buildInstance()
        {
          if (instance_)
            throw error::Fatal("Attempt to double-create a singleton service. "
                               "Either the application logic, or the compiler "
                               "or runtime system is seriously broken"
                              ,error::LUMIERA_ERROR_LIFECYCLE);
          
          // place new instance into embedded buffer
          instance_.reset (new TAR{});
          return instance_.get();
        }
    };
  
  template<typename ABS>
  class InstanceHolder<ABS,  enable_if<std::is_abstract<ABS>>>
    {
    public:
      ABS*
      buildInstance()
        {
          throw error::Fatal("Attempt to create a singleton instance of an abstract class. "
                             "Application architecture or lifecycle is seriously broken.");
        }
    };
}//(End)Implementation helper



template<class SRV>
class DependInject;

template<class SRV>
class Depend
  {
  public:
    using Factory = std::function<SRV*()>;
    
    static SRV* instance;
    static Factory factory;
    
    static InstanceHolder<SRV> singleton;
    
    friend class DependInject<SRV>;
    
    SRV&
    operator() ()
      {
        if (!instance)
          retrieveInstance();
        ENSURE (instance);
        return *instance;
      }
    
  private:
    void
    retrieveInstance()
      {
        ClassLock<SRV> guard;
        
        if (!instance)
          {
            if (!factory)
              {
                instance = singleton.buildInstance();
                factory = disabledFactory;
              }
            else
              instance = factory();
          }
      }
    
    static SRV*
    disabledFactory()
      {
        throw error::Fatal("Service not available at this point of the Application Lifecycle"
                          ,error::LUMIERA_ERROR_LIFECYCLE);
      }
  };


template<class SRV>
SRV* Depend<SRV>::instance;

template<class SRV>
typename Depend<SRV>::Factory Depend<SRV>::factory;

template<class SRV>
InstanceHolder<SRV> Depend<SRV>::singleton;


///////////////////////////////////////////////////////Configuration

template<class SRV>
class DependInject
  {
  public:
    
    template<class SUB>
    void
    useSingleton()
      {
        UNIMPLEMENTED ("reconfigure to plant a singleton of subclass type");
      }
    
    template<class IMP>
    class ServiceInstance
      {
      public:
        ServiceInstance()
          {
            
          }
      };
    
    template<class IMP>
    class Local
      {
      public:
        Local()
          {
            
          }
      };
  };


///////////////////////////////////////////////////////Usage

struct Dum
  : boost::noncopyable
  {
    virtual ~Dum() { }
    virtual int probe()  =0;
  };

  
int checksum = 0;

template<int N>
struct Dummy
  : Dum
  {
    Dummy() { checksum += N; }
   ~Dummy() { checksum -= N; }
    
    virtual int
    probe()
      {
        return N * checksum;
      }
  };



int
main (int, char**)
  {
    Depend<Dummy<1>> dep11;
    Depend<Dummy<5>> dep5;
    Depend<Dummy<1>> dep12;
    
    cout << "Siz-DUM : " << lib::test::showSizeof(dep11) << " " << lib::test::showSizeof(dep5) << endl;
    cout << "check-vor="<<checksum<<endl;
    
    SHOW_EXPR( dep11().probe() );
    SHOW_EXPR( checksum );
    SHOW_EXPR( dep5().probe() );
    SHOW_EXPR( checksum );
    SHOW_EXPR( dep12().probe() );
    SHOW_EXPR( checksum );
    
    Depend<Dum> dumm;
//  Depend<Dum>::factory = [](){ return nullptr; };
    SHOW_EXPR( dumm().probe() );
    
    
    cout <<  "\n.gulp.\n";
    
    return 0;
  }