Computed Read-Only Property vs. Function in Swift

In Swift, both computed read-only properties and functions are used to encapsulate logic and return values, but they serve slightly different purposes and can be chosen based on specific design requirements. Understanding their differences is crucial for designing clean and efficient Swift code.

Computed Read-Only Property

A computed property in Swift does not store a value directly. Instead, it provides a getter to calculate a value when accessed. If a computed property is read-only, it means that it only has a getter without a corresponding setter.

Declaration

Here’s how you can declare a computed read-only property:

• No Stored Value: It does not store any value. The value is computed each time the property is accessed.
• Read-Only: The absence of `set` means the property can't be modified directly.
• Clarity and Conciseness: It promotes a concise syntax, often improving code readability when the property represents a characteristic intrinsically related to the model (e.g., area of a circle).
• Optimization by Compiler: The Swift compiler optimizes computed properties to avoid unnecessary recalculations when possible.
• Can Receive Parameters: Functions can take arguments, offering more flexibility for parameterized operations.
• Explicit Invocation: You explicitly call a function, making it apparent that a computation or side-effect is occurring.
• Versatile Operation: Functions are better suited for operations involving more complex logic or multiple parameters.
• Readability: For broader operations not strictly representing a structural feature, functions can be more semantically meaningful.
• Computed Property is advantageous in cases where the value is a derivative property logically tied to the instance's identity. For example, in a `Rectangle` type, a computed property called `perimeter` could represent the rectangle's perimeter, derived from its width and height.
• Function, on the other hand, is better suited where computation involves more logic, parameters, or when an explicit operational call is intended. For instance, a function `scale(by factor: Double)` can scale a graphic rectangle without altering the basic properties directly.