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Summary:

Instance variables should be allowable as as default parameter variables for a function.

Steps to Reproduce:

1. Create a class with a non-optional property
2. Add a method that takes a default parameter value as an argument
3. Set the non-optional property as the parameter’s default value

Expected Results:

I expect the property’s current value to be used as the parameter’s default value when the function is called.

Actual Results:

The code will not compile.

Note:

Swift appears to be looking for a class variable instead of an instance variable.

Sample Code:

Paste this code into Playground. Try the two different implementations of shrinkPayment(_:)

———— playground code ————

class CreditCard {
    var minimumPayment = 55_00 //in pennies
    var currentBalance = 1_250_00
    
    // This implementation of shrinkPayment works, but is verbose
    
    func shrinkPayment(desiredPayment : Int?) -> Int {
        if let desiredPayment = desiredPayment {
            return currentBalance < desiredPayment ? currentBalance : desiredPayment
        } else {
            return currentBalance < minimumPayment ? currentBalance : minimumPayment
        }
    }
    
    // This implementation of shrinkPayment would be more concise, but doesn't work because instance variables can't be default parameter values

//    func shrinkPayment(desiredPayment : Int = minimumPayment) -> Int {
//        return currentBalance < desiredPayment ? currentBalance : desiredPayment
//    }

    func pay(amount : Int) {
        currentBalance -= amount
    }
}

let visa = CreditCard()

while visa.currentBalance > 0 {
    let payment = visa.shrinkPayment(nil)
    visa.pay(payment)
}

———— end playground code ————