英文:
Cannot use (*struct) as (*interface) in field value
问题
我有以下代码：
// eventloop.go
type Object interface {
ActivateSlot(name string, parameters vector.Vector);
}
// main.go
import loop "./eventloop"
// ...
const slotname = "printer"
type printer struct {
slot loop.Slot;
}
func (p *printer) Init() {
p.slot = loop.Slot{slotname, p}; // offending line
}
func (p *printer) ActivateSlot(name string, parameters vector.Vector) {
fmt.Println("Slot called: ", name);
}
当我尝试编译时，我得到以下错误：
jurily@jurily ~/workspace/go $ ./build.sh
main.go:23: cannot use p (type *printer) as type *eventloop.Object in field value
如果我将有问题的行注释掉，它可以编译和运行正常。这里发生了什么？我漏掉了什么？
英文:
I have the following code:
// eventloop.go
type Object interface {
ActivateSlot(name string, parameters vector.Vector);
}
// main.go
import loop "./eventloop"
// ...
const slotname = "printer"
type printer struct {
slot loop.Slot;
}
func (p *printer) Init() {
p.slot = loop.Slot{slotname, p}; // offending line
}
func (p *printer) ActivateSlot(name string, parameters vector.Vector) {
fmt.Println("Slot called: ", name);
}
When I try to compile, I get the following error:
jurily@jurily ~/workspace/go $ ./build.sh
main.go:23: cannot use p (type *printer) as type *eventloop.Object in field value
If I comment the offending line out, it compiles and runs fine. What's happening here? What am I missing?
答案1
得分: 4
更新：
这段代码在这里编译正常（都在同一个包中）：
type Object interface {
ActivateSlot(name string, parameters vector.Vector);
}
type Slot struct {
name string;
stuff Object;
}
const slotname = "printer"
type printer struct {
slot Slot;
}
func (p *printer) Init() {
p.slot = Slot{slotname, p}; // 有问题的那一行
}
func (p *printer) ActivateSlot(name string, parameters vector.Vector) {
fmt.Println("调用了Slot：", name);
}
看起来你遗漏了一点，*printer 是 Object 类型，而你试图将它赋值给类型为 *Object 的字段，这是不同的类型。
在大多数情况下，你可以像上面那样编写代码 - 不使用指向接口类型的指针 - 但是如果你必须这样做，你可以这样编译：
type Slot struct {
name string;
stuff *Object;
}
func (p *printer) Init() {
var o Object = p;
p.slot = Slot{slotname, &o}; // 有问题的那一行
}
所以 p 是一个 Object，你需要取 p 的地址来匹配 *Object 的规范。
英文:
Update:
This code compiles fine here (all in the same package):
type Object interface {
ActivateSlot(name string, parameters vector.Vector);
}
type Slot struct {
name string;
stuff Object;
}
const slotname = "printer"
type printer struct {
slot Slot;
}
func (p *printer) Init() {
p.slot = Slot{slotname, p}; // offending line
}
func (p *printer) ActivateSlot(name string, parameters vector.Vector) {
fmt.Println("Slot called: ", name);
}
It seems that what you are missing is that *printer is of type Object, and you are trying to assign it to a field of type *Object, which is a different type.
In most cases you would write it like above - without pointers to interface types - but if you have to, you can make it compile like this:
type Slot struct {
name string;
stuff *Object;
}
func (p *printer) Init() {
var o Object = p;
p.slot = Slot{slotname, &o}; // offending line
}
So p is an Object, you need to take the address of p to match the *Object specification.
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