What's the difference between Self vs self?

Sources & Resources

Main Source: 🔗 Ace the iOS Interview

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Further Reading:

TL/DR

In the context of protocols and extensions, Self refers to the type that conforms to the protocol whereas self refers to the value inside that type.

Consider this extension:

extension Int {
// Self here refers to the conforming type (Int)
func square() -> Self {
// self refers to the value of the Int itself i.e. 2
self * self
}
}

// self in the code above would now equal 2
let width = 2

// Output: 4
print(width.square())

Additionally, you can use Self to limit the conformance of a protocol to only specific types:

protocol Squareable where Self: Numeric {
    func square() -> Self
}

extension Squareable {
func square() -> Self {
    self * self
    }
}

Now, our Squareable protocol is only available to types that conform to Numeric.