Understand Properties in Swift

Properties associate values with a particular class, structure, or enumeration.

There are two type of properties in Swift:

• Stored: Constant and variable values are stored as part of an instance.
• Computed: A value is calculated rather than store.

Note: Enumerations can only have computed properties.

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Stored Properties:

Stored properties can be either variable stored properties (with var keyword) or constant stored properties (with the let keyword).

A default value for a stored property can be given in definition like

Or values can be set or modified during initialization.

Constant instances Stored Properties:

As structure is value type so when its instance is created as constant then all its properties too can not be modified.

But this is not the case with classes, if a class instance is declared as constant still its properties can be modified because of the class reference type behavior.

Lazy Stored Properties:

A lazy stored property is a property whose initial value is not calculated until the first time it is used. A stored property can be declared as lazy by writing the lazy modifier before its declaration.

Two important things to note:

• A lazy property can never be a constant as a constant property must always have a value before initialization completes.
• There is no guarantee that the lazy property will be initialized only once in multithreading environment.

Computed Properties:

Classes, structures, and enumerations can define computed properties, which calculates a value rather than storing a value. They provide a getter and optional setter.

• Computed properties must have explicit type declared.

• Computed properties must always be declared as var beacuse its value is never fixed.
• Code inside the getter runs everytime the property is called.
• Setter of computed property can modify another property.

Getter declaration:

To declare the getter for computed properties you need to define properties with get{}. The getter allows you to read data from the computed property.

Whenever a computed property will be accessed its getter will be called.

Setter declaration:

To set the value of a computed property, you need to define properties with set{}. If there is no setter defined for property then you can not set its value.

Note: If a computed property’s setter doesn’t define a name for the new value to be set, a default name of newValueis used.

Read-Only Computed Properties:

A computed property with a getter but no setter is known as a read-only computed property. A read-only computed property always returns a value, and can be accessed through dot syntax, but cannot be set to a different value.