On 11/13/13 3:57 AM, Kevin Ballard wrote:
On Nov 11, 2013, at 11:43 PM, Patrick Walton <[email protected]
<mailto:[email protected]>> wrote:
We considered Go's anonymous fields but rejected them because they
don't support virtual methods at the same time as field embedding.
I don’t follow. Why do Go’s anonymous fields not support virtual methods
at the same time as field embedding?
I want to write this but I can't:
package main
import "fmt"
type A struct {
x int
}
type B struct {
A
y int
}
type C struct {
A
z int
}
func(self *B) Foo() {
fmt.Printf("Hello!")
}
func(self *B) Upcast() *A {
return &self.A
}
func(self *C) Foo() {
fmt.Printf("Goodbye!")
}
func(self *C) Upcast() *A {
return &self.A
}
func main() {
myArray := []*A {
(&B { A: A { x: 1 }, y: 2 }).Upcast(),
(&C { A: A { x: 3 }, z: 4 }).Upcast(),
}
for i := 0; i < 2; i++ {
myArray[i].Foo()
}
}
Error:
prog.go:41: myArray[i].Foo undefined (type *A has no field or
method Foo)
You can't really write the thing you need to write inside `Upcast` to
make this code work. You would need to use an interface instead, but
then interfaces don't support shared fields, just like in Rust, leading
to the same problem.
Patrick
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