Either the docs or implementation are wrong.

This crashes (after a few second pause burning CPU):

$ cat gob.go
package main

import (
    "bytes"
    "gob"
    "log"
    "os"
)

type BlobRef struct {
    foo, bar string
}

func (br *BlobRef) String() string {
    if br == nil {
        return "<nil BlobRef>"
    }
    return br.foo + "-" + br.bar
}

func (br *BlobRef) GobEncode() ([]byte, os.Error) {
    log.Printf("GobEncode")
        return []byte(br.String()), nil
}

func (br *BlobRef) GobDecode(b []byte) os.Error {
    if br == nil {
        panic("nil receiver in GobDecode")
    }
    log.Printf("GobDecode(%q)", string(b))
    br.foo = "foo"
    br.bar = "bar"
    return nil
}

func main() {
    br := &BlobRef{"foo", "bar"}
    log.Printf("blobref String = %q", br)

    buf := new(bytes.Buffer)
    e := gob.NewEncoder(buf)
    err := e.Encode(br)
        if err != nil {
        log.Fatalf("Encode: %v", err)
        }

    d := gob.NewDecoder(buf)
        var got *BlobRef
        err = d.Decode(&got)
        if err != nil {
        log.Fatalf("Decode: %v", err)
        }
    if got == nil {
                log.Fatalf("got == nil")
        }

    if got.String() != br.String() {
                log.Fatalf("got = %q, want %q", got, br)
    }
    log.Printf("got = %q", &got)
}


$ gorun gob.go
2011/09/16 17:30:30 blobref String = "foo-bar"
2011/09/16 17:30:30 GobEncode
2011/09/16 17:30:30 GobDecode("foo-bar")
unexpected fault address 0x0
throw: fault
[signal 0xb code=0x80 addr=0x0 pc=0x409172]

goroutine 1 [running]:
main.(*BlobRef).String(0xf840000740, 0x45e7b0, 0xf8400002b8, 0x0)
    /home/bradfitz/goplay/gob.go:18 +0x7d
main.main()
    /home/bradfitz/goplay/gob.go:57 +0x427



$ hg identify
849002209017 tip

Attachments:

1. gob.go (1089 bytes)