encoding/gob: lazily initialize registerBasics

Defer call to registerBasics until the first invocation of NewDecoder() or NewEncoder()

This saves ~13.5kB of allocation in init()

Updates golang#26775

src/encoding/gob/decoder.go

@@ -39,6 +39,8 @@ type Decoder struct {
 // If r does not also implement io.ByteReader, it will be wrapped in a
 // bufio.Reader.
 func NewDecoder(r io.Reader) *Decoder {
+	registerBasics()
+
 	dec := new(Decoder)
 	// We use the ability to read bytes as a plausible surrogate for buffering.
 	if _, ok := r.(io.ByteReader); !ok {

src/encoding/gob/encoder.go

@@ -31,6 +31,8 @@ var spaceForLength = make([]byte, maxLength)
 
 // NewEncoder returns a new encoder that will transmit on the io.Writer.
 func NewEncoder(w io.Writer) *Encoder {
+	registerBasics()
+
 	enc := new(Encoder)
 	enc.w = []io.Writer{w}
 	enc.sent = make(map[reflect.Type]typeId)

src/encoding/gob/type.go

@@ -280,7 +280,6 @@ func init() {
 		panic(fmt.Sprintln("nextId too large:", nextId))
 	}
 	nextId = firstUserId
-	registerBasics()
 	wireTypeUserInfo = userType(reflect.TypeOf((*wireType)(nil)))
 }
 
@@ -874,40 +873,44 @@ func Register(value interface{}) {
 	RegisterName(name, value)
 }
 
+var registerBasicsOnce sync.Once
+
 func registerBasics() {
-	Register(int(0))
-	Register(int8(0))
-	Register(int16(0))
-	Register(int32(0))
-	Register(int64(0))
-	Register(uint(0))
-	Register(uint8(0))
-	Register(uint16(0))
-	Register(uint32(0))
-	Register(uint64(0))
-	Register(float32(0))
-	Register(float64(0))
-	Register(complex64(0i))
-	Register(complex128(0i))
-	Register(uintptr(0))
-	Register(false)
-	Register("")
-	Register([]byte(nil))
-	Register([]int(nil))
-	Register([]int8(nil))
-	Register([]int16(nil))
-	Register([]int32(nil))
-	Register([]int64(nil))
-	Register([]uint(nil))
-	Register([]uint8(nil))
-	Register([]uint16(nil))
-	Register([]uint32(nil))
-	Register([]uint64(nil))
-	Register([]float32(nil))
-	Register([]float64(nil))
-	Register([]complex64(nil))
-	Register([]complex128(nil))
-	Register([]uintptr(nil))
-	Register([]bool(nil))
-	Register([]string(nil))
+	registerBasicsOnce.Do(func() {
+		Register(int(0))
+		Register(int8(0))
+		Register(int16(0))
+		Register(int32(0))
+		Register(int64(0))
+		Register(uint(0))
+		Register(uint8(0))
+		Register(uint16(0))
+		Register(uint32(0))
+		Register(uint64(0))
+		Register(float32(0))
+		Register(float64(0))
+		Register(complex64(0i))
+		Register(complex128(0i))
+		Register(uintptr(0))
+		Register(false)
+		Register("")
+		Register([]byte(nil))
+		Register([]int(nil))
+		Register([]int8(nil))
+		Register([]int16(nil))
+		Register([]int32(nil))
+		Register([]int64(nil))
+		Register([]uint(nil))
+		Register([]uint8(nil))
+		Register([]uint16(nil))
+		Register([]uint32(nil))
+		Register([]uint64(nil))
+		Register([]float32(nil))
+		Register([]float64(nil))
+		Register([]complex64(nil))
+		Register([]complex128(nil))
+		Register([]uintptr(nil))
+		Register([]bool(nil))
+		Register([]string(nil))
+	})
 }