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
// 04/18 - investigate construction of static template members


/** @file try.cpp
 * Investigation: static initialisation order -- especially of static template member fields.
 * This version embeds the factory as Meyer's Singleton into the Front-Template using it, and
 * it invokes the factory from within the Front<TY> constructor -- thereby ensuring the factory
 * is indeed initialised prior to any usage and its lifespan extends beyond the lifespan of the
 * last instance using it.
 */

typedef unsigned int uint;

#include "lib/format-cout.hpp"
#include "lib/test/test-helper.hpp"



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


  
template<typename T>
class Factory
  {
  public:
    T val;
    
    Factory()
      : val{}
      {
        cout << "Factory-ctor  val="<<val<<endl;
      }
  };


template<typename T>
class Front
  {
  public:
    Factory<T>&
    fac()
      {
        static Factory<T> fac;
        return fac;
      }
    
    
    Front()
      {
        cout << "Front-ctor    val="<<fac().val<<endl;
        fac().val += 100;
      }
    
    T&
    operate ()
      {
        cout << "Front-operate val="<<fac().val<<endl;
        ++ fac().val;
        return fac().val;
      }
  };

//template<typename T>
//Factory<T> Front<T>::fac;


namespace {
  Front<int> front;
  
  int
  staticFun()
  {
    cout << "staticFun"<<endl;
    return front.operate() += 10;
  }
  
  int global_int = front.operate();
}



int
main (int, char**)
  {
    
    cout << "make-Front<int>..."<<endl;
    Front<int> fint;
    
    int& i = fint.operate();
    cout << "main:         val="<<i<<endl;
    cout << "main: staticFun..."<<staticFun()<<endl;
    cout << "global_int.......="<<global_int<<endl;
    
    cout <<  "\n.gulp.\n";
    
    return 0;
  }