Ohm Force Developer LibraryFlip Programming Guide

Flip Programming Guide

• About Flip Programming Guide
• Designing your Flip Application
• Writing a Flip Class Part 1
• Writing a Flip Class Part 2
• Using Containers
• Using Enums
• Using Blobs
• Using ObjectRefs
• Using Cues
• Navigating the Model
• Writing a DocumentObserver
• Writing a DocumentValidator
• Using the Undo/Redo system
• Managing Pseudo Const Members
  • Concepts
  • Transforming the Code
• Using an ObjectMold
• Writing a Converter
• Writing a DocumentTweaker

Managing Pseudo Const Members

This chapter will describe how to make a member (pseudo) const .

In the following, we will show the step by step construction of an hypothetic MyClass class.

Concepts

The Flip framework does not support const members inherently, that is declaring, for example, a ohm::flip::Int64 member as const won’t let you chance to assign a value. The member would always be 0 .

To circumvant this limitation, it was introduced the concept of post contruction stage . The post construction stage is called just after a Flip object is created, and before the object can be manipulated by the client. This stage allows to manage pseudo const members in Flip.

Typically pseudo const members have the same access API as normal members, except that they have no setter. To set the actual value of the member, the post construction stage is used, and will be called once by Flip when the object is created.

Transforming the Code

This section will show how to transform the code for a regular member with its setter/getter/changed members to a pseudo const member.

Declarative Code

The following listing shows the original declarative code, before it is modified to make the member _my_float a pseudo const member.

#include "ohm/flip/Object.h"

#include "ohm/flip/Float64.h"

class MyClass

:  public ohm::flip::Object

{

public:

   static void          declare ();

                        MyClass (ohm::flip::DocumentBase & document);

   virtual              ~MyClass () {}

   void                 ext_set_my_float (float val);

   float                get_my_float () const;

   bool                 my_float_changed () const;

private:

   ohm::flip::Float64   _my_float;

};

The following listing shows the modified declarative code, after it is modified to make the member _my_float a pseudo const member : ext_set_my_float was replaced by the virtual method ctor .

#include "ohm/flip/Object.h"

#include "ohm/flip/Float64.h"

class MyClass

:  public ohm::flip::Object

{

public:

   static void          declare ();

                        MyClass (ohm::flip::DocumentBase & document);

   virtual              ~MyClass () {}

   virtual void         ctor (flip::Args & args);

   float                get_my_float () const;

   bool                 my_float_changed () const;

private:

   ohm::flip::Float64   _my_float;

};

Implementation Code

The following listing shows the original implementation code, before it is modified to make the member _my_float a pseudo const member.

void  MyClass::ext_set_my_float (float val)

{

   _my_float = val;

}

float MyClass::get_my_float () const

{

   return _my_float;

}

bool  MyClass::my_float_changed () const

{

   return _my_float.did_value_change ();

}

The following listing shows the modified implementation code, after it is modified to make the member _my_float a pseudo const member : ext_set_my_float was replaced by the virtual method ctor .

void  MyClass::ctor (flip::Args & args)

{

   _my_float.ctor (args);

}

float MyClass::get_my_float () const

{

   return _my_float;

}

bool  MyClass::my_float_changed () const

{

   return _my_float.did_value_change ();

}

Calling Code

The following listing shows the original calling code, before it is modified to make the member _my_float a pseudo const member. The class is always created by the mean of insert into a container.

MyClassColl::iterator   MySuperClass::ext_add_element (float val)

{

   MyClassColl::iterator it = _class_coll.insert ();

   MyClassColl & my_class = *it;

   my_class.ext_set_my_float (val);

   return it;

}

The following listing shows the modified calling code, after it is modified to make the member _my_float a pseudo const member : ext_set_my_float was replaced by the use of a flip::Args object.

MyClassColl::iterator   MySuperClass::ext_add_element (float val)

{

   MyClassColl::iterator it = _class_coll.insert (

      flip::Args ().push (val)

   );

   return it;

}

The class flip::Args will behave like a parameter list holder, and acts like a FIFO queue. The exact same number of pushed values must be popped.

If the Flip class has one or more base class, the Flip framework code will automatically call the base classes with the same rule as for the constructor of C++ classes.