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)