C++ also comes with a large standard library that includes several container classes. Similarly, Objective-C adds object-oriented programming, dynamic typing, and reflection to C. If a category declares a method with the same method signature as an existing method in a class, the category’s method is adopted. Thus categories can not only add methods to a class, but also replace existing methods.
The run-time system in Objective C is a critical part of the language. The capabilities and implementation of the run-time component of Objective C tends to vary between compilers more than other features of the language. Instance methods have full access to the instance variables of the class. Control over instance variable access is provided via the @public, @protected, and @private directives. Instance variables declared with the @protected directive are accessible to instances of the class and subclasses of the class.
Dot notation is used only with property names, not with method names. File names should reflect the name of the class implementation that they
contain—including case. When the style guide allows multiple options it is preferable to pick one option
over mixed usage of multiple options. Using one style consistently throughout a
codebase lets engineers focus on other (more important) issues. Consistency also
enables better automation because consistent code allows more efficient
development and operation of tools that format or refactor code.
Declaring a Class with the Interface
The language is a superset of the C language, providing constructs to allow you to define classes and objects. Once you get the hang of the Smalltalk-style syntax, if you’ve programmed in an object-oriented language before, things should look fairly familiar. However, there are some differences, and I discuss them in this chapter.
If you don’t explicitly inherit from some class, your class becomes a root class. (In Objective-C, there can be many root classes.) That’s probably not what you want to do, because creating a root class is a very tricky and advanced topic that is only useful in very specific situations. In most cases, you will want to inherit from Object or some class that inherits from Object, etc. If you develop in NeXTStep / GNUstep / Cocoa, you will mostly be using another root class called NSObject, which provides different basic methods than Object.
Swift wasn’t built on the C programming language, so it can combine all the keywords and pull out the multiple @ symbols when an Objective-C type or object-related keyword is present. As mentioned above, in ARC, we need not add release and retain methods since that will be taken care by the compiler. Actually, the underlying process of Objective-C is still the same.
Constants need to be initialized when declaring them, and variables need to be initialized before use. If you take a look at the following code, you will notice that x was assigned an Optional value of 2014. This means that Swift compiler was aware that x might also be nil. The purpose of this tutorial is to give Objective-C developers a quick overview of new Swift language features, helping you take the next step and begin adopting Swift in your everyday work.
This also provides an opportunity to reuse the code functionality and fast implementation time. It is only possible with the properties swift vs objective c performance we can access the instance variables of the class. Actually, internally getter and setter methods are created for the properties.
Because of this, the more general term used in Swift reference is instance, which applies to any of these two. It is a good practice to you add a prefix to your classes and types too. There is no strict check from the compiler, so you can omit it, but it’s better not to. They are
similar to standard C functions, but in addition to executable code
they may also contain variable bindings to automatic (stack) or
managed (heap) memory.
If you do use them, please
document exactly which methods you expect to throw. Since internal methods are not really private, it’s easy to accidentally
override a superclass’s “private” method, thus making a very difficult bug to
squash. In general, private methods should have a fairly unique name that will
Objective-C Classes & Objects
prevent subclasses from unintentionally overriding them. It is important for those who might be subclassing your class that the
designated initializer be clearly identified. That way, they only need to
- It’s important to understand data encapsulation since it’s one of the core features of all Object-Oriented Programming (OOP) languages including Objective-C.
- The above example just uses a string operation, but it can have many features like encryption/decryption and so on.
- Sometimes, you may find that you wish to extend an existing class by adding behavior that is useful only in certain situations.
- As in Objective-C and C, use structs when you need to group a few values, and expect them to be copied rather than referenced.
override a single initializer (of potentially several) to guarantee the
initializer of their subclass is called. It also helps those debugging your
class in the future understand the flow of initialization code if they need to
step through it.