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
// 08/18 - Segfault when compiling some regular expressions for EventLog search
// 10/18 - investigate insidious reinterpret cast
// 12/18 - investigate the trinomial random number algorithm from the C standard lib
// 04/19 - forwarding tuple element(s) to function invocation
// 06/19 - use a statefull counting filter in a treeExplorer pipeline
// 03/20 - investigate type deduction bug with PtrDerefIter
// 01/21 - look for ways to detect the presence of an (possibly inherited) getID() function
// 08/22 - techniques to supply additional feature selectors to a constructor call


/** @file try.cpp
 * Investigate techniques to supply additional descriptive ctor arguments in a type safe way.
 * The idea is to provide friend functors, which might tweak or reset internal settings;
 * these functors are packaged into free standing friend functions with intuitive naming,
 * which, on call-site, look like algebraic expressions/data-types.
 * 
 * If desired, this mechanism can be mixed-in and integrated into a constructor call,
 * thus optionally allowing for arbitrary extra qualifiers, even with extra arguments.
 * @see builder-qualifier-support.hpp (wrapped as support lib)
 */

typedef unsigned int uint;


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

#include <functional>




template<class TAR>
class PropertyQualifierSupport
  {
  protected:
    using Manipulator = std::function<void(TAR&)>;
    
    struct Qualifier
      : Manipulator
      {
        using Manipulator::Manipulator;
      };

    template<class... QUALS>
    friend void qualify(TAR& target, Qualifier& qualifier, QUALS& ...qs)
    {
      qualifier(target);
      qualify(target, qs...);
    }
    
    friend void qualify(TAR&){ }

  public:
    // default construct and copyable
  };


class Feat
  : PropertyQualifierSupport<Feat>
  {
    
    friend Qualifier bla();
    friend Qualifier blubb(string);

  public:
    Feat() = default;
    
    template<class... QS>
    Feat(Qualifier qual, QS... qs)
      : Feat{}
      {
        qualify(*this, qual, qs...);
      }
    
    operator string ()  const
      {
        return "Feat{"+prop_+"}";
      }
    
  private:
    string prop_{"∅"};
  };


Feat::Qualifier
bla()
{
  return Feat::Qualifier{[](Feat& feat)
                            {
                              feat.prop_ = "bla";
                            }};
}

Feat::Qualifier
blubb(string murks)
{
  return Feat::Qualifier{[=](Feat& feat)
                            {
                              feat.prop_ += ".blubb("+murks+")";
                            }};
}


int
main (int, char**)
  {
    Feat f0;
    SHOW_EXPR(f0);
    
    Feat f1(bla());
    SHOW_EXPR(f1);
    
    Feat f2(blubb("Ψ"));
    SHOW_EXPR(f2);
    
    Feat f3(bla(),blubb("↯"));
    SHOW_EXPR(f3);
    
    Feat f4(blubb("💡"), bla());  // Note: evaluated from left to right, bla() overwrites prop
    SHOW_EXPR(f4);
    
    cout <<  "\n.gulp.\n";
    return 0;
  }