Chapter 4. Code generation with templates

KDevelop uses templates for generating source code files and to avoid writing repeatable code.

Creating a new class

The most common use for code generation is probably writing new classes. To create a new class in an existing project, right click on a project folder and choose Create from Template. The same dialog can be started from the menu by clicking FileNew from Template, but using a project folder has the benefit of setting a base URL for the output files. Choose Class in the category selection view, and the desired language and template in the other two views. After you have selected a class template, you will have to specify the details of the new class.



First you have to specify an identifier for the new class. This can be a simple name (like Bus) or a complete identifier with namespaces (like Transportation::Bus). In the latter case, KDevelop will parse the identifier and correctly separate the namespaces from the actual name. On the same page, you can add base classes for the new class. You may notice that some templates choose a base class on their own, you are free to remove it and/or add other bases. You should write the full inheritance statement here, which is language-dependent, such as public QObject for C++, extends SomeClass for PHP or simply the name of the class for Python.



In the next page, you are offered a selection of virtual methods from all inherited classes, as well as some default constructors, destructors and operators. Checking the check box next to a method signature will implement this method in the new class.

Clicking Next brings up a page where you can add members to a class. Depending on the selected template, these may appear in the new class as member variables, or the template may create properties with setters and getters for them. In a language where variable types have to be declared, such as C++, you have to specify both the type and the name of the member, such as int number or QString name. In other languages, you may leave out the type, but it is good practice to enter it anyway, because the selected template could still make some use of it.



In the following pages, you can choose a license for you new class, set any custom options required by the selected template, and configure output locations for all the generated files. By clicking Finish, you complete the assistant and create the new class. The generated files will be opened in the editor, so you can start adding code right away.

After creating a new C++ class, you will be given an option of adding the class to a project target. Choose a target from the dialog page, or dismiss the page and add the files to a target manually.

If you chose the Qt Object template, checked some of the default methods, and added two member variables, the output should look like on the following picture.



You can see that data members are converted into Qt properties, with accessor functions and the Q_PROPERTY macros. Arguments to setter functions are even passed by const-reference, where appropriate. Additionally, a private class is declared, and a private pointer created with Q_DECLARE_PRIVATE. All this is done by the template, choosing a different template in the first step could completely change the output.