Dynamic dispatch vs Final

When working with classes in Swift, it gives you ability to override superclass methods and properties, which basically means that the compiler would have to infer for method/property implementation at runtime and perform direct call or indirect access, this technique is called Dynamic dispatch.

This technique increases performance overhead for a performance sensitive application.

We will see how we can reduce the dynamism by using final

Consider the following example:

class BankAccount {
    var balance: Double = 100000.0
    var interestRate: Double = 7.5
    
    func calculateInterest() {
        let interest = balance + (balance * interestRate/100)
        print(interest)
    }
    
    func performSecretOperation() {
        calculateInterest()
        print("this is secret implmention")
    }
}


let start = CFAbsoluteTimeGetCurrent()
var account = BankAccount()

for i in stride(from: 0.0, through: 3600000, by: 1.0) {
    account.performSecretOperation()
}
let diff = CFAbsoluteTimeGetCurrent() - start
print("Took \(diff) seconds")         

Before explaining how making the class final could impact, I would love to share how much

I ran the above code with different limits, 360, 3600, ... and following are the results

here is the graphical representation of the impact in seconds

Now let's talk about het how it just making the class final can reduce the execution time by ~47 sec in simple operations when done at larger count.

Making the class final, clears compiler head to look for any other implementation as now no other class could inherit and override any of the method, making is a static dispatch.