how to overload an assignment operator in swift

Question

I would like to override the '=' operator for a CGFloat like the follow try :

func = (inout left: CGFloat, right: Float) {
    left=CGFloat(right)
}

So I could do the following:

var A:CGFloat=1
var B:Float=2
A=B

Can this be done ? I get the error Explicitly discard the result of the closure by assigning to '_'

Answer 1

That's not possible - as outlined in the documentation:

It is not possible to overload the default assignment operator (=). Only the compound assignment operators can be overloaded. Similarly, the ternary conditional operator (a ? b : c) cannot be overloaded.

If that doesn't convince you, just change the operator to +=:

func +=(left: inout CGFloat, right: Float) {
    left += CGFloat(right)
}

and you'll notice that you will no longer get a compilation error.

The reason for the misleading error message is probably because the compiler is interpreting your attempt to overload as an assignment

Answer 2

You can not override assignment but you can use different operators in your case. For example &= operator.

func &= (inout left: CGFloat, right: Float) {
    left = CGFloat(right)
}

So you could do the following:

var A: CGFLoat = 1
var B: Float = 2
A &= B

By the way operators &+, &-, &* exist in swift. They represent C-style operation without overflow. More

Answer 3

This is not operator overload approach. But the result may be what you are expecting

// Conform to `ExpressibleByIntegerLiteral` and implement it
extension String: ExpressibleByIntegerLiteral {
    public init(integerLiteral value: Int) {
        // String has an initializer that takes an Int, we can use that to
        // create a string
        self = String(value)
    }
}

extension Int: ExpressibleByStringLiteral {
    public init(stringLiteral value: String) {
        self = Int(value) ?? 0
    }
}

// No error, s2 is the string "4"
let s1: Int = "1"
let s2: String = 2

print(s1)
print(s2)
print(s1 + 2)