CH11.3 OK

eBook/11.3.md

@@ -0,0 +1,96 @@
+# 11.3 <20><><EFBFBD>μ<EFBFBD><CEBC><EFBFBD><EFBFBD><EFBFBD>ת<EFBFBD><D7AA><EFBFBD>ӿڱ<D3BF><DAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͣ<EFBFBD><CDA3><EFBFBD><EFBFBD>Ͷ<EFBFBD><CDB6><EFBFBD>
+
+һ<EFBFBD><EFBFBD><EFBFBD>ӿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>͵ı<EFBFBD><EFBFBD><EFBFBD> `varI` <20>п<EFBFBD><D0BF>԰<EFBFBD><D4B0><EFBFBD><EFBFBD>κ<EFBFBD><CEBA><EFBFBD><EFBFBD>͵<EFBFBD>ֵ<EFBFBD><D6B5><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD>ַ<EFBFBD>ʽ<EFBFBD><CABD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> **<EFBFBD><EFBFBD>̬** <20><><EFBFBD>ͣ<EFBFBD><CDA3><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD>ڱ<EFBFBD><DAB1><EFBFBD><EFBFBD>д洢<D0B4><E6B4A2>ֵ<EFBFBD><D6B5>ʵ<EFBFBD><CAB5><EFBFBD><EFBFBD><EFBFBD>͡<EFBFBD><CDA1><EFBFBD>ִ<EFBFBD>й<EFBFBD><D0B9><EFBFBD><EFBFBD>ж<EFBFBD>̬<EFBFBD><CCAC><EFBFBD>Ϳ<EFBFBD><CDBF>ܻ<EFBFBD><DCBB><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ͬ<EFBFBD><CDAC><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǿ<EFBFBD><C7BF>Է<EFBFBD><D4B7><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ӿڱ<D3BF><DAB1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>͡<EFBFBD>ͨ<EFBFBD><CDA8><EFBFBD><EFBFBD><EFBFBD>ǿ<EFBFBD><C7BF><EFBFBD>ʹ<EFBFBD><CAB9> **<EFBFBD><EFBFBD><EFBFBD>Ͷ<EFBFBD><EFBFBD><EFBFBD>** <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ij<EFBFBD><C4B3>ʱ<EFBFBD><CAB1> `varI` <20>Ƿ<EFBFBD><C7B7><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> `T` <20><>ֵ<EFBFBD><D6B5>
+
+```go
+    v := varI.(T)       // unchecked type assertion
+```
+
+**varI<72><49><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><D2BB><EFBFBD>ӿڱ<D3BF><DAB1><EFBFBD>**<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ᱨ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>`invalid type assertion: varI.(T) (non-interface type (type of varI) on left)` <20><>
+
+<EFBFBD><EFBFBD><EFBFBD>Ͷ<EFBFBD><EFBFBD>Կ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ч<EFBFBD>ģ<EFBFBD><EFBFBD><EFBFBD>Ȼ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ᾡ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ת<EFBFBD><EFBFBD><EFBFBD>Ƿ<EFBFBD><EFBFBD><EFBFBD>Ч<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ԥ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>еĿ<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ԡ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ת<EFBFBD><EFBFBD><EFBFBD>ڳ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱʧ<EFBFBD>ܻᵼ<EFBFBD>´<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȫ<EFBFBD>ķ<EFBFBD>ʽ<EFBFBD><EFBFBD>ʹ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʽ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ͷ<EFBFBD><EFBFBD>ԣ<EFBFBD>
+
+```go
+if v, ok := varI.(T); ok {  // checked type assertion
+    Process(v)
+    return
+}
+// varI is not of type T
+```
+
+<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ת<EFBFBD><EFBFBD><EFBFBD>Ϸ<EFBFBD><EFBFBD><EFBFBD>`v` <20><> `varI` ת<><D7AA><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> `T`<EFBFBD><EFBFBD>ֵ<EFBFBD><EFBFBD>`ok` <20><><EFBFBD><EFBFBD> `true`<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> `v` <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> `T` <20><><EFBFBD><EFBFBD>ֵ<EFBFBD><D6B5>`ok` <20><> `false`<EFBFBD><EFBFBD>Ҳû<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʱ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+
+**Ӧ<><D3A6><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ʹ<EFBFBD><CAB9><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ķ<EFBFBD>ʽ<EFBFBD><CABD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ͷ<EFBFBD><CDB6><EFBFBD>**<EFBFBD><EFBFBD>
+
+<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>£<EFBFBD><EFBFBD><EFBFBD><EFBFBD>ǿ<EFBFBD><EFBFBD><EFBFBD>ֻ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> `if` <20>в<EFBFBD><D0B2><EFBFBD>һ<EFBFBD><D2BB> `ok` <20><>ֵ<EFBFBD><D6B5><EFBFBD><EFBFBD>ʱʹ<CAB1><CAB9><EFBFBD><EFBFBD><EFBFBD>µķ<C2B5><C4B7><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EEB7BD><EFBFBD>ģ<EFBFBD>
+
+```go
+if _, ok := varI.(T); ok {
+    // ...
+}
+```
+
+TODO ??<3F><>In this form shadowing the variable varI by giving varI and v the same name is sometimes done.
+
+ʾ<EFBFBD><EFBFBD> 11.4 type_interfaces.go
+
+```go
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+type Square struct {
+	side float32
+}
+
+type Circle struct {
+	radius float32
+}
+
+type Shaper interface {
+	Area() float32
+}
+
+func main() {
+	var areaIntf Shaper
+	sq1 := new(Square)
+	sq1.side = 5
+
+	areaIntf = sq1
+	// Is Square the type of areaIntf?
+	if t, ok := areaIntf.(*Square); ok {
+		fmt.Printf("The type of areaIntf is: %T\n", t)
+	}
+	if u, ok := areaIntf.(*Circle); ok {
+		fmt.Printf("The type of areaIntf is: %T\n", u)
+	} else {
+		fmt.Println("areaIntf does not contain a variable of type Circle")
+	}
+}
+
+func (sq *Square) Area() float32 {
+	return sq.side * sq.side
+}
+
+func (ci *Circle) Area() float32 {
+	return ci.radius * ci.radius * math.Pi
+}
+```
+
+<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+
+    The type of areaIntf is: *main.Square
+    areaIntf does not contain a variable of type Circle
+
+<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ж<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> `Circle`<EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ҳʵ<EFBFBD><EFBFBD><EFBFBD><EFBFBD> `Shaper` <20>ӿڡ<D3BF> `t, ok := areaIntf.(*Square); ok ` <20><><EFBFBD><EFBFBD> `areaIntf` <20><><EFBFBD>Ƿ<EFBFBD>һ<EFBFBD><D2BB><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 'Square' <20><><EFBFBD>͵ı<CDB5><C4B1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ȷ<EFBFBD><C8B7><EFBFBD>ģ<EFBFBD>Ȼ<EFBFBD><C8BB><EFBFBD><EFBFBD><EFBFBD>Dz<EFBFBD><C7B2><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƿ<EFBFBD><C7B7><EFBFBD><EFBFBD><EFBFBD>һ<EFBFBD><D2BB> 'Circle' <20><><EFBFBD>͵ı<CDB5><C4B1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Ƿ񶨵ġ<F1B6A8B5>
+
+**<EFBFBD><EFBFBD>ע**
+
+<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> `areaIntf.(*Square)` <20>е<EFBFBD> `*` <20>ţ<EFBFBD><C5A3>ᵼ<EFBFBD>±<EFBFBD><C2B1><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>`impossible type assertion: Square does not implement Shaper (Area method has pointer receiver)`
+
+- [Ŀ¼](directory.md)
+- <20><>һ<EFBFBD>£<EFBFBD>[11.2 <20>ӿ<EFBFBD>Ƕ<EFBFBD>׽ӿ<D7BD>](11.2.md)
+- <20><>һ<EFBFBD>ڣ<EFBFBD>[11.4 <20><><EFBFBD><EFBFBD>switch](11.4.md)

eBook/directory.md

@@ -96,6 +96,7 @@
 - 第11章：[接口（interface）与反射（reflection）](11.0.md)
     - 11.1 [接口是什么](11.1.md)
     - 11.2 [接口嵌套接口](11.2.md)
+    - 11.3 [11.3 如何检测和转换接口变量的类型：类型断言](11.3.md)
 
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