URL StaticString

URLStaticString.swift

extension URL {
    init(_ staticString: StaticString) {
        if let url = URL(string: "\(staticString)") {
            self = url
        } else {
            preconditionFailure("'\(staticString)' does not represent a legal URL")
        }
    }
}

static let urlString = "http://hello"

// New version
static let url = URL(urlString) 

// Old version
static let url = URL(string: "http://hello")! // Need !