go - Expecting nil but getting an interface with a nil value in return, which should be nil -

go - Expecting nil but getting an interface with a nil value in return, which should be nil -

run @ http://play.golang.org/p/sl12vfs9vp

package main import "fmt" func main() { err := run() if err != nil { fmt.printf("%#v", err) } } func run() (err error) { homecoming check() } func check() *result { homecoming nil } type result struct { message string } func (result *result) error() string { homecoming result.message }

this discussed on faq , go traps website:

an interface value nil if inner value , type both unset, (nil, nil). in particular, nil interface hold nil type. if store pointer of type *int within interface value, inner type *int regardless of value of pointer: (*int, nil). such interface value hence non-nil when pointer within nil.

(...)

to homecoming proper nil error caller, function must homecoming explicit nil:

func returnserror() error { if bad() { homecoming errbad } homecoming nil }

go