Int 不能转换为 T

Question

I have the following protocol

public protocol NumericType {
    static func +(lhs: Self, rhs: Self) -> Self
    static func addWithOverflow(_ lhs: Self, _ rhs: Self) -> (Self, overflow: Bool)
}

Also I am extending Int to conforms to it as follows

extension Int : NumericType { }

Then I have a struct with the following definition

struct State<T:NumericType>  {

    let current : T

    init(current : T) {

        self.current = current
    }

    static func initial() -> State<T> {

        return State(current: 0) // Int is not convertible to T
    }
}

Answer 1

NumericType does not promise that it is ExpressibleByIntegerLiteral , so there's no way to convert 0 (which is assumed to be an Int here) to T . Your protocol needs to provide some .zero that it knows it can initialize with (or it needs to conform to ExpressibleByIntegerLiteral ).