Xcode显示警告:Switch condition evaluates to a constant

 
 `
 import UIKit
 
 
enum Barcode
 {
 case UPCA(Int,Int,Int,Int)
 case QRCode(String)
 }
 
 
class ViewController: UIViewController,UITextViewDelegate
 {
 override func viewDidLoad()
 {
 var productBarcode = Barcode.UPCA(123, 456, 789, 0)
 productBarcode = Barcode.QRCode("xyz")
 //Xcode⚠️Switch condition evaluates to a constant
 //警告:Switch 条件被判断为一个常量.
 //可能是编译器认为变量在函数内部是不变的吧
 switch productBarcode
 {
 case let .UPCA(a, b, c, d):
 print(a,b,c,d)
 case let .QRCode(str):
 print(str)
 }
 }
 }
 `
 
 

解决方法:
将变量从函数内部提取出来,如下

 
 `
 import UIKit
 
 
enum Barcode
 {
 case UPCA(Int,Int,Int,Int)
 case QRCode(String)
 }
 
 
class ViewController: UIViewController,UITextViewDelegate
 {
 var productBarcode = Barcode.UPCA(123, 456, 789, 0)
 override func viewDidLoad()
 {
 productBarcode = Barcode.QRCode("xyz")
 
 
    switch productBarcode
    {
    case let .UPCA(a, b, c, d):
        print(a,b,c,d)
    case let .QRCode(str):
        print(str)
    }
}
 
 
}
 `