CODEWITHSUNDEEP
swift
Andrej
Andrej

Reputation: 7426

ClosedRange second parameter to be smaller and return nil

I'm trying to create an extension to the ClosedRange type, that would return nil if the second parameter is lower than the first parameter.

I'm thinking to make something that could be used like this: myClosedRange = ClosedRange.safe(4,3)

I've created an extension like this:

extension ClosedRange {
    static func safe(_ lhs: Int, _ rhs: Int) -> ClosedRange<Int>? {
        guard lhs >= 0, rhs >= lhs else {
            return nil
        }
        return lhs ... rhs
    }
}

But when I try to use it like this: let myRange = ClosedRange.safe(4, 3), I'm getting the error: Generic parameter 'Bound' could not be inferred

I don't understand the error and don't know how to fix it? Any suggestion?

Upvotes: 0

Views: 147

Answers (1)

vadian
vadian

Reputation: 285092

Specify the generic type

let myRange = ClosedRange<Int>.safe(4, 3)

or constrain the Range accordingly

extension ClosedRange where Bound : Comparable, Bound : ExpressibleByIntegerLiteral {
    static func safe(_ lhs: Bound, _ rhs: Bound) -> ClosedRange<Bound>? {
        guard lhs >= 0, rhs >= lhs else {
            return nil
        }
        return lhs ... rhs
    }
}

Upvotes: 1

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