encoding/gob: cannot decode into top-level interface type #2367
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Owner changed to @robpike. Status changed to Accepted. |
In gob streams, values to be encoded as interfaces must be sent as interfaces. In this case, a struct is being sent and an interface is requested for the decode. This program is therefore incorrect and in general cannot easily be made to work since the sender has not explained the required interface specification in the stream. Open to suggestions: 1) document this property better 2) provide better error message (although all the information is in the existing message, it could always be clearer) 3) possibly make it work in cases where it can, specifically an empty interface receiver. I do not favor this. |
I think it would be worth making this work - it's the classic use case of a stream of differently typed messages. Requiring a container type just to get around this restriction seems a bit silly to me. However, looking at the protocol I do see the problem. Better documentation is probably the answer. |
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This issue was closed by revision ba576b2. Status changed to Fixed. |
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Issue #2938 has been merged into this issue. |
mikioh
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This issue was closed.
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This program fails because it cannot decode a (correctly registered) type into a *interface{}. I can't see anything in the documentation that prohibits this, though I think it's a reasonable use-case even it does. output of program: fail: gob: wrong type received for local value *interface { }: Foo = struct { } 06199863489f+ tip package main import ( "os" "fmt" "gob" "io" ) type Foo struct { } func main() { gob.Register(Foo{}) r, w := io.Pipe() go func() { e := gob.NewEncoder(w) e.Encode(Foo{}) w.Close() }() d := gob.NewDecoder(r) for { var v interface{} if err := d.Decode(&v); err != nil { fmt.Printf("fail: %v\n", err) os.Exit(1) } fmt.Printf("got %v of type %T\n", v, v) } }The text was updated successfully, but these errors were encountered: