Explanation:
In Swift, class extensions and categories (known as extensions in Swift) are used to add additional functionality to a class. However, they have some limitations compared to Objective-C.
One of the limitations is that class extensions and extensions in Swift do not support the use of the +load method. The +load method is a special method in Objective-C that gets called automatically when a class or category is loaded into memory.
In Swift, the equivalent functionality to +load method is achieved using lazily initialized static variables or properties. These variables are initialized only once when they are first accessed.
Example:
// Swift class with extension
class MyClass {
static var myStaticVariable: Int = {
// This block is equivalent to +load method
print("MyClass loaded into memory.")
return 10
}()
}
extension MyClass {
func myExtensionMethod() {
print("Extension method called.")
}
}
// Usage
let value = MyClass.myStaticVariable // Prints "MyClass loaded into memory."
let instance = MyClass()
instance.myExtensionMethod() // Prints "Extension method called."
In the example above, we define a class MyClass with a static variable myStaticVariable. The initialization block for the static variable is equivalent to the +load method in Objective-C.
We also define an extension for MyClass that adds a method myExtensionMethod. This method can be called on instances of MyClass.
When we access the static variable myStaticVariable for the first time, the initialization block will be executed and the message “MyClass loaded into memory.” will be printed.
Similarly, when we call the myExtensionMethod on an instance of MyClass, the message “Extension method called.” will be printed.