There is no native way to disable copying in Go. So if you have a structure that you want the user to not be able to copy, but only pointer pass to ensure global uniqueness, you can do that by defining a structure called noCopy
and implementing the sync.Locker
interface.
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// noCopy may be embedded into structs which must not be copied
// after the first use.
//
// See https://golang.org/issues/8005#issuecomment-190753527
// for details.
type noCopy struct{}
// Lock is a no-op used by -copylocks checker from `go vet`.
func (*noCopy) Lock() {}
func (*noCopy) UnLock() {}
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Then embed noCopy
into your custom structure and go vet
will do the checking for us.
As an example.
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package main
import (
"fmt"
)
type noCopy struct{}
func (*noCopy) Lock() {}
func (*noCopy) Unlock() {}
type Demo struct {
noCopy noCopy
}
func Copy(d Demo) {
CopyTwice(d)
}
func CopyTwice(d Demo) {}
func main() {
d := Demo{}
fmt.Printf("%+v", d)
Copy(d)
fmt.Printf("%+v", d)
}
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The execution results are as follows.
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$ go vet main.go
# command-line-arguments
./main.go:16: Copy passes lock by value: main.Demo contains main.noCopy
./main.go:17: call of CopyTwice copies lock value: main.Demo contains main.noCopy
./main.go:19: CopyTwice passes lock by value: main.Demo contains main.noCopy
./main.go:23: call of fmt.Printf copies lock value: main.Demo contains main.noCopy
./main.go:25: call of Copy copies lock value: main.Demo contains main.noCopy
./main.go:27: call of fmt.Printf copies lock value: main.Demo contains main.noCopy
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