golang如何检查某个类型是否实现了某个接口

type I interface{
    ......
}

type T struct{}

var _ I = T{}       // Verify that T implements I.
var _ I = (*T)(nil) // Verify that *T implements I.

如果T（或*T，相应地） 没有实现 I，错误将在编译时被发现。

也可以直接类型断言

type WriterTo interface {
    WriteTo(w Writer) (n int64, err error)
}

// If the reader has a WriteTo method, use it to do the copy.
// Avoids an allocation and a copy.
if wt, ok := src.(WriterTo); ok {
	return wt.WriteTo(dst)
}