Lightning talk from iOSDevUK 2014

1. Currying in Swift
A tale of state encapsulation
Maxim Zaks @iceX33

2. Every presentation
needs a theme

3. func amountWithVat(vat:Float, amount: Float) -> Float {
return roundf((1 + vat) * amount)
}
let amount1 = amountWithVat(0.19, 100)
let amount2 = amountWithVat(0.19, 200)
let amount3 = amountWithVat(0.2, 300)

4. func amountWithVat(vat:Float)(amount: Float) -> Float {
return roundf((1 + vat) * amount)
}
let addGermanVatTo = amountWithVat(0.19)
let addUKVatTo = amountWithVat(0.2)
let amount1 = addGermanVatTo(amount: 100)
let amount2 = addGermanVatTo(amount: 200)
let amount3 = addUKVatTo(amount: 300)

5. func amountWithVat( vat : Float,
roundFunction : (Float)->Float = roundf)
(amount: Float) -> Float {
return roundFunction((1 + vat) * amount)
}
let addGermanVatTo = amountWithVat(0.19){
roundf($0 * 100) / 100
}
let addUKVatTo = amountWithVat(0.2)
let amount1 = addGermanVatTo(amount: 101)
let amount2 = addGermanVatTo(amount: 200)
let amount3 = addUKVatTo(amount: 300)

6. Should we consider
currying as a
revelation?

7. func amountWithVat(vat:Float)(amount: Float) -> Float {
return roundf((1 + vat) * amount)
}
let addGermanVatTo = amountWithVat(0.19)
let addUKVatTo = amountWithVat(0.2)
let amount1 = addGermanVatTo(amount: 100)
let amount2 = addGermanVatTo(amount: 200)
let amount3 = addUKVatTo(amount: 300)

8. func amountWithVat(vat:Float) -> Float -> Float {
return { (amount:Float) -> Float in
return roundf((1 + vat) * amount)
}
}
let addGermanVatTo = amountWithVat(0.19)
let addUKVatTo = amountWithVat(0.2)
let amount1 = addGermanVatTo(100)
let amount2 = addGermanVatTo(200)
let amount3 = addUKVatTo(300)

9. typedef float (^FloatToFloat)(float);
FloatToFloat (^amountWithVat)(float) =
^FloatToFloat (float vat) {
return ^(float amount){
return roundf((1 + vat) * amount);
};
};
FloatToFloat addGermanVatTo = amountWithVat(.19);
FloatToFloat addUKVatTo = amountWithVat(0.2);
float amount1 = addGermanVatTo(100);
float amount2 = addGermanVatTo(200);
float amount3 = addUKVatTo(300);

10. Interesting application of function currying found out
by Ole Begemann
(http://oleb.net/blog/2014/07/swift-instance-methods-curried-functions/)

11. class BankAccount {
var balance: Double = 0.0
func deposit(amount: Double) {
balance += amount
}
}
let account = BankAccount()
account.deposit(100) // balance is now 100
let depositor = BankAccount.deposit
depositor(account)(100) // balance is now 200

12. So every method is implemented internaly through
function currying

13. One More Thing

14. Who knows the name
of the show I used for
the theme

16. Thank you
Maxim Zaks @iceX33