Go.Method+Go.Interface

# Go.Method + Go.Interface Presented in Women Who Code, Taipei , 2021  slide: https://hackmd.io/@pieceofr/S1uweajlt --- This presentation is base on - [A Tour of Go : Method + Interface Section](https://tour.golang.org/methods/1) - [簡中版本](https://tour.go-zh.org/welcome/1) --- ## Method & Interface - NOT a Object Oriented Language (OOP) - Encapsulation - Inheritance - Polymorphism - Overloading (diff params) - Overriding (child overides its parent) - GO has Method + Interface --- ### Method - 方法(method)即函數(function) - a function with receiver - reciever before function name - 使用 Dot(.) 來操作 receiver - 限制: Reciever 只能定義在同一個 package (ps. codes in bottom page) ---- - Method version ```go= type Vertex struct {X, Y float64} func (v Vertex) Abs() float64 { return math.Sqrt(v.X*v.X + v.Y*v.Y) } ``` - Function version ```go= func Abs(v Vertex) float64 { return math.Sqrt(v.X*v.X + v.Y*v.Y) } ``` ---- 如何為不是 package 裡的 struct 寫方法 ? https://tour.golang.org/methods/3 --- ### Pointer - 使用pointer 當 reciever - func (v *MyStruct) Method1() float64 - 本身不能是 pointer (ie. MyStruct 不能是 pointer) - 使用 pointer 是可以改變 Reciever的值 - Excercise on https://tour.golang.org/methods/4 - 把 Scale 的 Reciever 變為 struct - pointer 跟 struct 的不同是 ? - (2 mins and share) ---- - call indirection ```go func (v *Vertex) Scale(f float64) v := Vertex{3, 4} p := &Vertex{4, 3} v.Scale() // (&p).Scale() p.Scale() ``` - go throgh https://tour.golang.org/methods/7 to understand ---- Receiver : Value or Pointer ? - Pointer - 改變值 - 避免重複 copy value 更有效率 - Value - Next Section --- ### Interface - An interface type is defined as a set of method signatures - 是由一组方法签名定义的集合 ```go= type I interface { M() } type T struct {S string} // 此方法表示类型 T 实现了接口 I，但我们无需显式声明此事。 func (t T) M() { fmt.Println(t.S) } func main() { var i I = T{"hello"} i.M() } ``` - Decoupling definition 跟 implementation ---- - 在 Interface 執行方法時必須是確實的型別 - Interface Vaue 跟特定型別綁定 - https://play.golang.org/p/ciKrbglFF8o ---- interface 要如何處理 reciever 空值!? (Interface values with nil underlying values) ```go= var iNil I var tNil *T iNil = tNil iNil.M() func (t *T) M() { // t = nil 時可以進入程式 if t == nil { // Take care of it fmt.Println("<nil>") return } fmt.Println(t.S)//如果nil 卻沒處理呼叫 method 會當掉 } ``` ---- The empty interface ```interface{}``` 沒有任何方法的 interface ```go= // fmt.Print func Println(a ...interface{}) (n int, err error) { // ... } ``` --- ### Type Assertions - This statement asserts that the interface value i holds the concrete type T and assigns the underlying T value to the variable t ``` t := i.(T) ``` or ``` t, ok := i.(T) ``` --- ### Type Switch - A type switch is a construct that permits several type assertions in series ```go= func do(i interface{}) { switch v := i.(type) { case int: fmt.Printf("Twice %v is %v\n", v, v*2) case string: fmt.Printf("%q is %v bytes long\n", v, len(v)) default: fmt.Printf("I don't know about type %T!\n", v) } } ``` --- Excercise: Method and Interface ``` command line program that takes 2 arguments - flag s : shape string - Circle/Square - flag l : length - 大於 1 -> use the value - 其他＝ 1 - Shape interface - functions - Area() float64 - SetLength(l float64) - Fix PrintArea Function ``` - [Excercise Template](https://replit.com/@PieceofrPai/EexcerciseTemplate#main.go) - https://replit.com/join/iaupdralvj-pieceofrpai (join-link) - [Example](https://replit.com/@PieceofrPai/ExcerciseInterfaceMethod) --- Excercise: Errors - Sqrt參數小於0 回傳一個自定義的 ErrNegativeSqrt Error - [Excercise Discription](https://tour.golang.org/methods/20) - [My Sqrt Solution](https://play.golang.org/p/zd2s0neSXRu) - [My Excercise Errors](https://play.golang.org/p/g2sgNaQDPtY) --- ### Thank you! :sheep: You can find me on - [gitHub](github/pieceofr) - [email](pieceofr@gmail.com)