使用默认参数解密Swift协议扩展

所以我们可以说

• 如果变量推断类型为Protocol ，则将始终调用该方法的动态实现。
• 否则 ，将调用该方法的协议实现， 除非该方法不覆盖默认参数。

我与您分享了所有这些情况的操场片段：

protocol TheProtocol { 
 func method1(text: String) 
 } 
 
 extension TheProtocol { 
 func method1(text: String = "default1") { 
 print("Called method1 from TheProtocol: \(text)") 
 } 
 func method2(text: String = "default2") { 
 print("Called method2 from TheProtocol: \(text)") 
 } 
 } 
 
 struct Struct1: TheProtocol { 
 func method1(text: String = "default1") { 
 print("Called method1 from struct 1: \(text)") 
 } 
 
 func method2(text: String = "default2") { 
 print("Called method2 from struct 1: \(text)") 
 } 
 } 
 
 print("s1 is of type Struct1") 
 let s1 = Struct1() 
 s1.method1() 
 s1.method1(text: "CUSTOM") 
 s1.method2() 
 s1.method2(text: "CUSTOM") 
 
 print("s1 is of type TheProtocol") 
 let s2: TheProtocol = Struct1() 
 s2.method1() 
 s2.method1(text: "CUSTOM") 
 s2.method2() 
 s2.method2(text: "CUSTOM") 

它产生以下输出：

 s1 is of type Struct1 
 Called method1 from struct 1: default1 
 Called method1 from struct 1: CUSTOM 
 Called method2 from struct 1: default2 
 Called method2 from struct 1: CUSTOM 
 s1 is of type TheProtocol 
 Called method1 from TheProtocol: default1 
 Called method1 from struct 1: CUSTOM 
 Called method2 from TheProtocol: default2 
 Called method2 from TheProtocol: CUSTOM 

与上面共享的图一致。

结论

带有默认参数的Swift协议扩展方法乍一看似乎有些不清楚的行为，您可能会注意到您的某些扩展或实现方法从未被调用过，并且如果您到了本文的结尾，您可能会遇到这种情况。问题，我希望在看完上图之后，现在至少您的某些疑虑消失了。