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CH11.3 OK

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2015-08-28 12:52:38 +08:00
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# 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)