从 golang 中的 interface{} 正确转换类型断言失败

Question

这是我从下面的简单重现案例中得到的输出：2015/06/22 21:09:50 ok: false2015/06/22 21:09:50 stub: *main.Stub <nil>显然，存根被正确标记为指向存根类型的指针，但转换失败。我正在尝试更新数组的内容。package mainimport "log"const BUFFER_SIZE = 8type Value struct {    value int}func (v Value) Value() int          { return v.value }func (v *Value) SetValue(value int) { v.value = value }type Stub struct {    Value    testString string}type StubFactory struct{}type FactoryInterface interface {    NewInstance(size int) []interface{}}func (factory StubFactory) NewInstance(size int) []interface{} {    stubs := make([]interface{}, size)    for i, _ := range stubs {        stubs[i] = &Stub{Value: Value{i}, testString: ""}    }    return stubs}type Buffer struct {    values []interface{}}func NewBuffer(factory FactoryInterface, size int) *Buffer {    return &Buffer{values: factory.NewInstance(size)}}func (buf *Buffer) Get(index int) interface{} {    return &buf.values[index]}func main() {    stubFactory := &StubFactory{}    buffer := NewBuffer(stubFactory, BUFFER_SIZE)    index := 0    if stub, ok := buffer.Get(index).(*Stub); ok { // THIS FAILS :-(        log.Printf("ok: %+v\n", ok)        log.Printf("stub: %T %+v\n", stub, stub)        stub.SetValue(1234)        log.Printf("value:%+v\n", buffer.Get(index)) // I WANT "1234"    } else {        log.Printf("ok: %+v\n", ok)        log.Printf("stub: %T %+v\n", stub, stub) // but this shows the right type    }}

Answer 1

错误是：

func (buf *Buffer) Get(index int) interface{} {

    return &buf.values[index]

}

你想做：

func (buf *Buffer) Get(index int) interface{} {

    return buf.values[index]

}

当您返回 &buf.values[index] 时，您将返回一个指向接口的指针。哪个是 *(*Stub) （在某种意义上）