英文:
In Go, how do I pass a slice of interface to something that expects slice of a different compatible interface?
问题
我有两个接口，A和B。恰好A包含B。最后，我有一个A的具体实现（称为Impl），根据定义，它也实现了B。
例如：
type A interface {
Close() error
Read(b []byte) (int, error)
}
type Impl struct {}
func (I Impl) Read(b []byte) (int, error) {
fmt.Println("In read!")
return 10, nil
}
func (I Impl) Close() error {
fmt.Println("I am here!")
return nil
}
由于A要求Read()方法，而Impl实现了A，它也满足io.Reader接口。
如果我尝试将单个A对象传递给期望io.Reader的函数，它可以正常工作。但是，如果我尝试将[]A切片传递给期望[]io.Reader的函数，它会失败。
例如：
func single(r io.Reader) {
fmt.Println("in single")
}
func slice(r []io.Reader) {
fmt.Println("in slice")
}
im := &Impl{}
// 正常工作
single(im)
// 失败！
list := []A{im}
slice(list)
如果我可以将A传递给single(r io.Reader)函数，为什么不能将[]A传递给slice(r []io.Reader)函数，如何进行修正？
实际实现代码请参考：https://play.golang.org/p/QOREQJTQhD，只需取消main()函数中的最后两行的注释，就会显示错误信息：
main.go:38: cannot use list (type []A) as type []io.Reader in argument to slice
英文:
I have two interfaces, A and B. It happens that A includes B. Finally, I have a concrete implementation of A (call it Impl), which, by definition, also implements B.
For example:
type A interface {
Close() error
Read(b []byte) (int, error)
}
type Impl struct {}
func (I Impl) Read(b []byte) (int, error) {
fmt.Println("In read!")
return 10, nil
}
func (I Impl) Close() error {
fmt.Println("I am here!")
return nil
}
Since A requires Read(), and Impl implements A, it also satisfies io.Reader.
If I try to pass individual items across functions, it works fine. But if I try slices of A to functions expecting io.Reader, it fails.
Example:
func single(r io.Reader) {
fmt.Println("in single")
}
func slice(r []io.Reader) {
fmt.Println("in slice")
}
im := &Impl{}
// works
single(im)
// FAILS!
list := []A{t}
slice(list)
If I can pass an A to single(r io.Reader), why can I not pass []A to slice(r []io.Reader), and how would I correct it?
Actual implementation at https://play.golang.org/p/QOREQJTQhD just uncomment the last two lines in main() and the error shows:
main.go:38: cannot use list (type []A) as type []io.Reader in argument to slice
答案1
得分: 3
我在这里问了类似的问题：https://stackoverflow.com/questions/38525874/in-go-how-can-i-make-a-generic-function-with-slices
不幸的是，这绝对是 Go 语言的一个弱点。你唯一的解决办法是创建一个新的类型为 []io.Reader 的切片，并将元素从 []A 复制过去。
英文:
I kind of asked something similar here
https://stackoverflow.com/questions/38525874/in-go-how-can-i-make-a-generic-function-with-slices
Sadly, this is definitely a weakness in Go. The only way for you to go around this is to make a new slice of type []io.Reader with elements from []A
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