CODEWITHSUNDEEP
swiftswift3default-parametersoverriding
Joshua White
Joshua White

Reputation: 51

Swift - Overriding functions with different default parameters

Case: A base class (A) with a function (doSomething) that has a default parameter (param: T = foo), and a subclass (B) which overrides that function with a different default parameter (param: T = bar). But is then called as A.

Edit: Apologies for the original code, so actually what is happening is basically the following:

class Foo
{
    func doSomething(a: String = "123")
    {
        print(a)
    }
}

class Bar: Foo
{
    override func doSomething(a: String = "abc")
    {
        print("Using Bar method body... but not Bar's default a value!")
        print(a)
    }
}

(Bar() as Foo).doSomething()

// Prints:
// Using Bar method body... but not Bar's default a value!
// 123

Is it a bug or expected behaviour that it uses the functions body but doesn't use the functions default parameter?

Upvotes: 5

Views: 1639

Answers (1)

NonCreature0714
NonCreature0714

Reputation: 6024

It's being called as Foo (or A) because you tell it to. Because you're instantiating Bar() as Foo, it is doing exactly that.

If you do:

Bar().doSomething()

Bar's method is what is called:

Using Bar method body...
abc

Interestingly, as you point out:

(Bar() as Foo).doSomething()

Yields: 

Using Bar method body...
123

Because Bar is instantiated as Foo, (note emphasis) Bar gets Foo's default parameters, yet still executes Bar's function body.

Interesting observation!

Upvotes: 2

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