零/可选或没有..主差异是什么

Question

这两个代码的最大区别是什么？我完全是Swift/编码的初学者:) thx寻求帮助

func hellou(_ name: String = "World") -> String {
return "Hello (name)!"}

func hello(_ name: String? = nil) -> String {
return "Hello, (name ?? "World")!)}

Answer 1

这是一些简单的操场代码，可以演示差异：

import UIKit
func hellou(_ name: String = "World") -> String {
    return "Hello (name)!"}

func hello(_ name: String? = nil) -> String {
    return "Hello, (name ?? "World")!"
}

var someNonNilOptional:String? = "this is not nil, but it could be"
var someNilOptional:String?  // this is nil
var someNonNilString:String = "This string cannot be nil"

// First, all inputs work in the optional method
hello(someNilOptional) // this is fine because hello takes optionals
hello(someNonNilOptional) // this is also fine, because hello takes optionals
hello(someNonNilString) // this too is fine, because a string will work for an Optional(String)

// for the non-optional method, things get more dicey
hellou(someNonNilString) // this is fine, because the parameter is String not String?
hellou(someNonNilOptional!) // this works because we force-unwrap and it wasn't nil
hellou(someNilOptional!) // Fatal error: Unexpectedly found nil while unwrapping an Optional value
hellou(someNonNilOptional) // compile time error
hellou(someNilOptional) // compile time error

有时您不想要可选参数。上面的两个编译时间错误是我希望字符串具有程序员值的好示例，并且编译器确保它们是。