Closed
Description
What did you do?
example.com$ cat >./main.go <<EOF
package main
import (
"errors"
"fmt"
"net"
)
func main() {
const addr = "••••••••"
conn, err := net.Dial("tcp", addr)
if err != nil {
if errors.As(err, (*net.InvalidAddrError)(nil)) {
fmt.Println("invalid address: %s")
}
}
defer conn.Close()
}
EOF
example.com$ cat >./go.mod <<EOF
module example.com
go 1.12
EOF
example.com$ go version
go version devel +33fdc10a30 Wed Apr 17 13:37:58 2019 -0400 linux/amd64
example.com$ go run main.go
What did you expect to see?
errors.As being useful for type-checks even if I don't want to allocate space to store the result.
For this specific example:
invalid address: ••••••••
What did you see instead?
panic: errors: target must be a non-nil pointer
goroutine 1 [running]:
errors.As(0x54de60, 0xc000098000, 0x507020, 0x0, 0x0)
/usr/local/google/home/bcmills/go/src/errors/wrap.go:86 +0x5eb
main.main()
/tmp/tmp.8hp5hhWBDQ/example.com/main.go:13 +0xd5
exit status 2
This is the documented behavior of errors.As, but it seems strictly less useful than allowing a nil pointer of a concrete type.