to improve the chances for compatibility, open a window of unused ids

and specify a lowest id granted to users.

R=rsc
CC=golang-dev
https://golang.org/cl/186081

diff --git a/src/pkg/gob/type.go b/src/pkg/gob/type.go
index 2ffdfc6a1a700d1cc02665ab658454455195abac..ace80d6ad5a5e2bf0a49c62e731674530177374a 100644 (file)
--- a/src/pkg/gob/type.go
+++ b/src/pkg/gob/type.go
@@ -37,6 +37,7 @@ type typeId int32
 
 var nextId typeId       // incremented for each new type we build
 var typeLock sync.Mutex // set while building a type
+const firstUserId = 64  // lowest id number granted to user
 
 type gobType interface {
        id() typeId
@@ -101,6 +102,7 @@ var tString = bootstrapType("string", "", 6)
 var tWireType = mustGetTypeInfo(reflect.Typeof(wireType{})).id
 
 func init() {
+       // Some magic numbers to make sure there are no surprises.
        checkId(7, tWireType)
        checkId(9, mustGetTypeInfo(reflect.Typeof(commonType{})).id)
        checkId(11, mustGetTypeInfo(reflect.Typeof(structType{})).id)
@@ -109,6 +111,12 @@ func init() {
        for k, v := range idToType {
                builtinIdToType[k] = v
        }
+       // Move the id space upwards to allow for growth in the predefined world
+       // without breaking existing files.
+       if nextId > firstUserId {
+               panicln("nextId too large:", nextId)
+       }
+       nextId = firstUserId
 }
 
 // Array type