UUID+InitByInt.swift

import XCTest
import struct Foundation.UUID
extension UUID {
    internal init(_ uint8s: UInt8...) {
        var list:[UInt8] = Array(repeating: 0, count: 16)
        for (index, value) in uint8s.enumerated() where index < 16 {
            list[15-index] = value
        }
        self.init(list: list)
    }
    public init(n: Int) {
        self.init(u: n > 0 ? UInt(n) : 0)
    }
    public init(u: UInt) {
        var u = u
        var list:[UInt8] = Array(repeating: 0, count: 16)
        let u8Max = UInt(UInt8.max)
        var i = 15
        while u > 0 {
            list[i] = UInt8(u&u8Max)
            u >>= UInt8.bitWidth
            i -= 1
        }
        self.init(list: list)
    }
    private init(list: [uint8]) {
        let uuidT = (list[0],
                     list[01], list[02], list[03], list[04], list[05],
                     list[06], list[07], list[08], list[09], list[10],
                     list[11], list[12], list[13], list[14], list[15])
        self.init(uuid: uuidT)
    }
}
extension UUID: ExpressibleByIntegerLiteral {
    public init(integerLiteral value: Int) {
        self.init(n: value)
    }
}

final class UUIDsTests: XCTestCase {
    func testInitByInt_UInt() throws {
        XCTAssertEqual(UUID(n: 0).uuidString, "00000000-0000-0000-0000-000000000000")
        XCTAssertEqual(UUID(n: 1).uuidString, "00000000-0000-0000-0000-000000000001")
        XCTAssertEqual(UUID(n: 2).uuidString, "00000000-0000-0000-0000-000000000002")
        XCTAssertEqual(UUID(n: 3).uuidString, "00000000-0000-0000-0000-000000000003")
        XCTAssertEqual(UUID(n: 255).uuidString, "00000000-0000-0000-0000-0000000000FF")
        XCTAssertEqual(UUID(n: 256).uuidString, "00000000-0000-0000-0000-000000000100")
        XCTAssertEqual(UUID(n: .max).uuidString, "00000000-0000-0000-7FFF-FFFFFFFFFFFF")
        XCTAssertEqual(UUID(n: -1).uuidString, "00000000-0000-0000-0000-000000000000")
        XCTAssertEqual(UUID(u: .max).uuidString, "00000000-0000-0000-FFFF-FFFFFFFFFFFF")
    }
    func testNumberLiteral() throws {
        let expect = "00000000-0000-0000-0000-000000000011"
        
        assertUUID(17, expect)
        assertUUID(0_1_7, expect)
        assertUUID(0b10001, expect)
        assertUUID(0o21, expect)
        assertUUID(0x11, expect)
        
    }
    func testHelper() throws {
        XCTAssertEqual(UUID(1,1).uuidString, "00000000-0000-0000-0000-000000000101")
        XCTAssertEqual(UUID(1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1).uuidString, "01010101-0101-0101-0101-010101010101")
        XCTAssertEqual(UUID(1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1).uuidString, "01010101-0101-0101-0101-010101010101")
    }
    private func assertUUID(_ uuid: UUID, _ expect: String, message: String = "", file: StaticString = #filePath, line: UInt = #line) {
        XCTAssertEqual(uuid.uuidString, expect, message, file: file, line: line)
    }
}