Protocol declaration syntax in Swift - Step-by-Step Execution

Concept Flow - Protocol declaration syntax

Start Protocol Declaration

↓

Write 'protocol' keyword

↓

Name the Protocol

↓

Define Requirements (properties, methods)

↓

Close Protocol Declaration

↓

End

This flow shows how to declare a protocol: start with the keyword, name it, add required properties and methods, then close.

Execution Sample

Swift

protocol Vehicle {
    var numberOfWheels: Int { get }
    func drive()
}

Declares a protocol named Vehicle with a read-only property and a method requirement.

Execution Table

Step	Action	Code Part	Result
1	Start protocol declaration	protocol	Begin defining a protocol
2	Name the protocol	Vehicle	Protocol named Vehicle created
3	Declare property requirement	var numberOfWheels: Int { get }	Read-only property required
4	Declare method requirement	func drive()	Method drive() required
5	Close protocol declaration	}	Protocol Vehicle fully declared

💡 Protocol declaration ends after closing brace '}'

Variable Tracker

Element	Start	After Step 2	After Step 3	After Step 4	Final
Protocol Name	null	Vehicle	Vehicle	Vehicle	Vehicle
Properties	null	null	numberOfWheels (read-only)	numberOfWheels (read-only)	numberOfWheels (read-only)
Methods	null	null	null	drive()	drive()

Key Moments - 2 Insights

Why do we use { get } after the property declaration?

The { get } means the property must be readable (a getter), but it does not have to be writable. See execution_table step 3.

Can protocols contain code implementations inside?

No, protocols only declare requirements (like properties and methods), but do not provide code. This is shown in execution_table steps 3 and 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is declared at step 3?

A A read-only property requirement

B A method implementation

C The protocol name

D Closing the protocol

💡 Hint

Check the 'Code Part' and 'Result' columns at step 3 in execution_table

At which step is the protocol name defined?

A Step 1

B Step 2

C Step 4

D Step 5

💡 Hint

Look at the 'Action' and 'Code Part' columns in execution_table

If we add { get set } to the property, how would variable_tracker change?

A Protocol name would change

B Methods would change

C Properties would be writable and readable

D No change at all

💡 Hint

Refer to variable_tracker row 'Properties' and understand { get set } means read and write

Concept Snapshot

protocol ProtocolName {
    var propertyName: Type { get / get set }
    func methodName()
}
- Use 'protocol' keyword to declare
- Define required properties and methods
- Properties can be read-only ({ get }) or read-write ({ get set })

Full Transcript

This visual trace shows how to declare a protocol in Swift. First, write the keyword 'protocol', then name your protocol. Next, declare required properties with { get } to indicate read-only or { get set } for read-write. Then declare required methods without implementation. Finally, close the declaration with a brace. Protocols only specify what is required, not how it works.