ios - @property/@synthesize equivalent in swift

Question

We used to declare property to pass data between classes as following:

.h file (interface file)
@property (nonatomic) double topSpeed;

.m file (implementation file)
@synthesize topSpeed;

Now there is no interface class, how to pass data between .swift classes ?

Answer 1

Swift provides no differentiation between properties and instance variables (i.e, the underlying store for a property). To define a property, you simply declare a variable in the context of a class.

A swift class is simply a ClassName.swift file.

You declare a class and properties as

class SomeClass {

  var topSpeed: Double
  var aStrProperty: String
  var anIntProperty: Int

  //Initializers and other functions

}

You access property values via dot notation. As of Xcode6 beta 4, there also are access modifiers (public, internal and private) in Swift. By default every property is internal. See here for more information.

For more information, refer to the Swift Programming Guide:

Stored Properties and Instance Variables

If you have experience with Objective-C, you may know that it provides two ways to store values and references as part of a class instance. In addition to properties, you can use instance variables as a backing store for the values stored in a property.

Swift unifies these concepts into a single property declaration. A Swift property does not have a corresponding instance variable, and the backing store for a property is not accessed directly. This approach avoids confusion about how the value is accessed in different contexts and simplifies the property’s declaration into a single, definitive statement. All information about the property—including its name, type, and memory management characteristics—is defined in a single location as part of the type’s definition.