Consider this case:
package main
import (
"errors"
"fmt"
"sync"
)
type A struct {
Lock sync.Mutex
X int
}
type B struct {
A
Y int
}
func newA(x int) (A, error) {
if x > 0 {
return A{}, errors.New("x should not be positive")
}
return A{X: x}, nil
}
func newB(x int, y int) (B, error) {
a, err := newA(x)
if err != nil {
return B{}, err
}
return B{
A: a,
Y: y,
}, nil
}
func main() {
b, err := newB(-1, 3)
fmt.Println(b.Y)
fmt.Println(err)
}
Actually, there is no way to avoid struct copy if the struct containing
mutex is in another struct directly.
Run
go tool vet test.go
It will reports
test.go:32: literal copies lock value from a: main.A contains sync.Mutex
On Tuesday, December 13, 2016 at 3:16:14 AM UTC+8, Ian Lance Taylor wrote:
>
> On Sun, Dec 11, 2016 at 11:48 PM, <i...@liangsun.org <javascript:>>
> wrote:
> >
> > What about type embedding? If put a sync.Mutex in a struct, that struct
> can
> > not be embedded into another struct, right?
>
> That turns out not to be the case. You can embed that struct in
> another struct. But then, of course, you can not simply copy that
> other struct.
>
> > So I guess it's better idea to use structs with pointer to mutex.
>
> It depends.
>
> Ian
>
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