Kexi/Junior Jobs/Add d-pointers

maintainer of this task: staniek at kde.org
OPEN, DIFFICULTY=2/5
Recommended for Google Code-IN program

Goal

Improve internal APIs in Kexi. This can be done easily by introducing d-poitners to classes that lack them.

Introduction

Read section about d-pointers on Techbase (d-pointers only, not shared d-pointers).

Classes that have to be converted are in this form:

 // MyClass.h
 class MyClass {
 public:
  MyClass();
 private:
  Foo m_foo;
 };
 
 // MyClass.cpp
 MyClass::MyClass() {
  m_foo/doSomething();
 }

After converting to d-pointer it should be:

 // MyClass.h
 class MyClass {
 public:
  MyClass();
 private:
  class Private;
  Private * const d;
 };
 
 // MyClass.cpp
 class MyClass::Private {
 public:
  Private() 
  Foo foo;
 };
 
 MyClass::MyClass()
  : d(new Private)
 {
  d->foo.doSomething();
 }
 
 MyClass::~MyClass()
 {
  delete d;
 }

Further tasks

Converting non-trivial classes to use d-pointer may also require:

any code in the class' .cpp file referring to m_foo attribute should be changed to d->foo
if there were public or protected member variables, move them to the d-pointer class and add accessors and setters for them as in the example below. Read about guildelines for accessors and setters on Techbase.

 // MyClass.h
 class MyClass {
 public:
  MyClass();
  bool isBlack;
 };

After converting to d-pointer it should be:

 // MyClass.h
 class MyClass {
 public:
  MyClass();
  bool isBlack() const; // notice the const
  void setBlack(bool black);
 private:
  class Private;
  Private * const d;
 };
 
 // MyClass.cpp
 class MyClass::Private {
 public:
  Private() 
  bool isBlack;
 };
 
 MyClass::MyClass()
  : d(new Private)
 {
  d->foo.doSomething();
 }
 
 MyClass::~MyClass()
 {
  delete d;
 }
 
 bool isBlack() const
 {
  return d->isBlack;
 }
 void setBlack(bool black)
 {
  d->isBlack = black;
 }

The class typically should be "non-copyable" and thus add Q_DISABLE_COPY(...) line in private section of the class as presented below to avoid copying what would conflict with the d-pointer. This macro disables copy constructor and assignment operator. See the Qt docs for more information.

 class MyClass
 {                                                                   
  // ...
 private:
  Q_DISABLE_COPY(MyClass)
  // ...
 };

Alter any code outside of the class that uses the class' API so that the code compiles and runs in exactly the same way as before.
If there is inline code in header file that uses member variable, move the variable to d-pointer class if you know for sure the inline code isn't there for optimization. If unsure, ask the mentor or the task maintainer.
After the work is done, the code should be compiled and possibly the program should be executed to check if there are no regressions.

Required skills

Average C++ needed, at least begginner no Qt recommended.

Notes to mentor

This task can be naturally splited to many students but please have consistency in mind
Results are stored within a new branch kexi-dpointers-gci, should be created and maintained by mentor
The resulting patch should be also uploaded to http://git.reviewboard.kde.org
Mentor should synchronize students' work within the single branch
Please always emphasize importance of coding style to students and check that - it's so easier to maintain the style from day one instead of fixing afterwards. Show Techbase articles for that.
Take care of coding practices too (see Techbase articles)