api: the Decimal type is immutable

The patch forces the use of objects of type Decimal instead
of pointers.

Part of #238

Author: oleg-jukovec

CHANGELOG.md

@@ -24,6 +24,7 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 - Change encoding of the queue.Identify() UUID argument from binary blob to
   plain string. Needed for upgrade to Tarantool 3.0, where a binary blob is
   decoded to a varbinary object (#313).
+- Use objects of the Decimal type instead of pointers (#238)
 
 ### Deprecated
 

README.md

@@ -27,6 +27,7 @@ faster than other packages according to public benchmarks.
   * [API reference](#api-reference)
   * [Walking\-through example](#walking-through-example)
   * [Migration to v2](#migration-to-v2)
+    * [decimal package](#decimal-package)
     * [multi package](#multi-package)
     * [pool package](#pool-package)
     * [msgpack.v5](#msgpackv5)
@@ -148,6 +149,11 @@ by `Connect()`.
 
 The article describes migration from go-tarantool to go-tarantool/v2.
 
+#### decimal package
+
+Now you need to use objects of the Decimal type instead of pointers to it. A
+new constructor `MakeDecimal` returns an object. `NewDecimal` has been removed.
+
 #### multi package
 
 The subpackage has been deleted. You could use `pool` instead.

decimal/decimal.go

@@ -21,6 +21,7 @@ package decimal
 
 import (
 	"fmt"
+	"reflect"
 
 	"github.com/shopspring/decimal"
 	"github.com/vmihailenco/msgpack/v5"
@@ -42,54 +43,67 @@ const (
 	decimalPrecision = 38
 )
 
+var (
+	one decimal.Decimal = decimal.NewFromInt(1)
+	// -10^decimalPrecision - 1
+	minSupportedDecimal decimal.Decimal = maxSupportedDecimal.Neg().Sub(one)
+	// 10^decimalPrecision - 1
+	maxSupportedDecimal decimal.Decimal = decimal.New(1, decimalPrecision).Sub(one)
+)
+
 type Decimal struct {
 	decimal.Decimal
 }
 
-// NewDecimal creates a new Decimal from a decimal.Decimal.
-func NewDecimal(decimal decimal.Decimal) *Decimal {
-	return &Decimal{Decimal: decimal}
+// MakeDecimal creates a new Decimal from a decimal.Decimal.
+func MakeDecimal(decimal decimal.Decimal) Decimal {
+	return Decimal{Decimal: decimal}
 }
 
-// NewDecimalFromString creates a new Decimal from a string.
-func NewDecimalFromString(src string) (result *Decimal, err error) {
+// MakeDecimalFromString creates a new Decimal from a string.
+func MakeDecimalFromString(src string) (Decimal, error) {
+	result := Decimal{}
 	dec, err := decimal.NewFromString(src)
 	if err != nil {
-		return
+		return result, err
 	}
-	result = NewDecimal(dec)
-	return
+	result = MakeDecimal(dec)
+	return result, nil
 }
 
-// MarshalMsgpack serializes the Decimal into a MessagePack representation.
-func (decNum *Decimal) MarshalMsgpack() ([]byte, error) {
-	one := decimal.NewFromInt(1)
-	maxSupportedDecimal := decimal.New(1, decimalPrecision).Sub(one) // 10^decimalPrecision - 1
-	minSupportedDecimal := maxSupportedDecimal.Neg().Sub(one)        // -10^decimalPrecision - 1
-	if decNum.GreaterThan(maxSupportedDecimal) {
+func decimalEncoder(e *msgpack.Encoder, v reflect.Value) ([]byte, error) {
+	dec := v.Interface().(Decimal)
+	if dec.GreaterThan(maxSupportedDecimal) {
 		return nil,
 			fmt.Errorf(
 				"msgpack: decimal number is bigger than maximum supported number (10^%d - 1)",
 				decimalPrecision)
 	}
-	if decNum.LessThan(minSupportedDecimal) {
+	if dec.LessThan(minSupportedDecimal) {
 		return nil,
 			fmt.Errorf(
 				"msgpack: decimal number is lesser than minimum supported number (-10^%d - 1)",
 				decimalPrecision)
 	}
 
-	strBuf := decNum.String()
+	strBuf := dec.String()
 	bcdBuf, err := encodeStringToBCD(strBuf)
 	if err != nil {
 		return nil, fmt.Errorf("msgpack: can't encode string (%s) to a BCD buffer: %w", strBuf, err)
 	}
 	return bcdBuf, nil
 }
 
-// UnmarshalMsgpack deserializes a Decimal value from a MessagePack
-// representation.
-func (decNum *Decimal) UnmarshalMsgpack(b []byte) error {
+func decimalDecoder(d *msgpack.Decoder, v reflect.Value, extLen int) error {
+	b := make([]byte, extLen)
+	n, err := d.Buffered().Read(b)
+	if err != nil {
+		return err
+	}
+	if n < extLen {
+		return fmt.Errorf("msgpack: unexpected end of stream after %d decimal bytes", n)
+	}
+
 	// Decimal values can be encoded to fixext MessagePack, where buffer
 	// has a fixed length encoded by first byte, and ext MessagePack, where
 	// buffer length is not fixed and encoded by a number in a separate
@@ -111,10 +125,12 @@ func (decNum *Decimal) UnmarshalMsgpack(b []byte) error {
 	if exp != 0 {
 		dec = dec.Shift(int32(exp))
 	}
-	*decNum = *NewDecimal(dec)
+	ptr := v.Addr().Interface().(*Decimal)
+	*ptr = MakeDecimal(dec)
 	return nil
 }
 
 func init() {
-	msgpack.RegisterExt(decimalExtID, (*Decimal)(nil))
+	msgpack.RegisterExtDecoder(decimalExtID, Decimal{}, decimalDecoder)
+	msgpack.RegisterExtEncoder(decimalExtID, Decimal{}, decimalEncoder)
 }

decimal/decimal_test.go

@@ -63,10 +63,10 @@ func (t *TupleDecimal) DecodeMsgpack(d *msgpack.Decoder) error {
 		return err
 	}
 
-	if dec, ok := res.(*Decimal); !ok {
+	if dec, ok := res.(Decimal); !ok {
 		return fmt.Errorf("decimal doesn't match")
 	} else {
-		t.number = *dec
+		t.number = dec
 	}
 	return nil
 }
@@ -160,12 +160,12 @@ var decimalSamples = []struct {
 func TestMPEncodeDecode(t *testing.T) {
 	for _, testcase := range benchmarkSamples {
 		t.Run(testcase.numString, func(t *testing.T) {
-			decNum, err := NewDecimalFromString(testcase.numString)
+			decNum, err := MakeDecimalFromString(testcase.numString)
 			if err != nil {
 				t.Fatal(err)
 			}
 			var buf []byte
-			tuple := TupleDecimal{number: *decNum}
+			tuple := TupleDecimal{number: decNum}
 			if buf, err = msgpack.Marshal(&tuple); err != nil {
 				t.Fatalf(
 					"Failed to msgpack.Encoder decimal number '%s' to a MessagePack buffer: %s",
@@ -270,7 +270,7 @@ func TestEncodeMaxNumber(t *testing.T) {
 	referenceErrMsg := "msgpack: decimal number is bigger than maximum " +
 		"supported number (10^38 - 1)"
 	decNum := decimal.New(1, DecimalPrecision) // // 10^DecimalPrecision
-	tuple := TupleDecimal{number: *NewDecimal(decNum)}
+	tuple := TupleDecimal{number: MakeDecimal(decNum)}
 	_, err := msgpack.Marshal(&tuple)
 	if err == nil {
 		t.Fatalf("It is possible to msgpack.Encoder a number unsupported by Tarantool")
@@ -285,7 +285,7 @@ func TestEncodeMinNumber(t *testing.T) {
 		"supported number (-10^38 - 1)"
 	two := decimal.NewFromInt(2)
 	decNum := decimal.New(1, DecimalPrecision).Neg().Sub(two) // -10^DecimalPrecision - 2
-	tuple := TupleDecimal{number: *NewDecimal(decNum)}
+	tuple := TupleDecimal{number: MakeDecimal(decNum)}
 	_, err := msgpack.Marshal(&tuple)
 	if err == nil {
 		t.Fatalf("It is possible to msgpack.Encoder a number unsupported by Tarantool")
@@ -302,7 +302,7 @@ func benchmarkMPEncodeDecode(b *testing.B, src decimal.Decimal, dst interface{})
 	var buf []byte
 	var err error
 	for i := 0; i < b.N; i++ {
-		tuple := TupleDecimal{number: *NewDecimal(src)}
+		tuple := TupleDecimal{number: MakeDecimal(src)}
 		if buf, err = msgpack.Marshal(&tuple); err != nil {
 			b.Fatal(err)
 		}
@@ -327,13 +327,15 @@ func BenchmarkMPEncodeDecodeDecimal(b *testing.B) {
 func BenchmarkMPEncodeDecimal(b *testing.B) {
 	for _, testcase := range benchmarkSamples {
 		b.Run(testcase.numString, func(b *testing.B) {
-			decNum, err := NewDecimalFromString(testcase.numString)
+			decNum, err := MakeDecimalFromString(testcase.numString)
 			if err != nil {
 				b.Fatal(err)
 			}
 			b.ResetTimer()
 			for i := 0; i < b.N; i++ {
-				msgpack.Marshal(decNum)
+				if _, err := msgpack.Marshal(decNum); err != nil {
+					b.Fatal(err)
+				}
 			}
 		})
 	}
@@ -342,20 +344,20 @@ func BenchmarkMPEncodeDecimal(b *testing.B) {
 func BenchmarkMPDecodeDecimal(b *testing.B) {
 	for _, testcase := range benchmarkSamples {
 		b.Run(testcase.numString, func(b *testing.B) {
-			decNum, err := NewDecimalFromString(testcase.numString)
+			decNum, err := MakeDecimalFromString(testcase.numString)
 			if err != nil {
 				b.Fatal(err)
 			}
-			var buf []byte
-			if buf, err = msgpack.Marshal(decNum); err != nil {
+			buf, err := msgpack.Marshal(decNum)
+			if err != nil {
 				b.Fatal(err)
 			}
 			b.ResetTimer()
-			var v TupleDecimal
 			for i := 0; i < b.N; i++ {
-				msgpack.Unmarshal(buf, &v)
+				if err := msgpack.Unmarshal(buf, &decNum); err != nil {
+					b.Fatal(err)
+				}
 			}
-
 		})
 	}
 }
@@ -371,7 +373,7 @@ func tupleValueIsDecimal(t *testing.T, tuples []interface{}, number decimal.Deci
 		if len(tpl) != 1 {
 			t.Fatalf("Unexpected return value body (tuple len)")
 		}
-		if val, ok := tpl[0].(*Decimal); !ok || !val.Equal(number) {
+		if val, ok := tpl[0].(Decimal); !ok || !val.Equal(number) {
 			t.Fatalf("Unexpected return value body (tuple 0 field)")
 		}
 	}
@@ -447,9 +449,9 @@ func TestMPEncode(t *testing.T) {
 	samples = append(samples, benchmarkSamples...)
 	for _, testcase := range samples {
 		t.Run(testcase.numString, func(t *testing.T) {
-			dec, err := NewDecimalFromString(testcase.numString)
+			dec, err := MakeDecimalFromString(testcase.numString)
 			if err != nil {
-				t.Fatalf("NewDecimalFromString() failed: %s", err.Error())
+				t.Fatalf("MakeDecimalFromString() failed: %s", err.Error())
 			}
 			buf, err := msgpack.Marshal(dec)
 			if err != nil {
@@ -481,7 +483,7 @@ func TestMPDecode(t *testing.T) {
 			if err != nil {
 				t.Fatalf("Unmsgpack.Marshalling failed: %s", err.Error())
 			}
-			decActual, ok := v.(*Decimal)
+			decActual, ok := v.(Decimal)
 			if !ok {
 				t.Fatalf("Unable to convert to Decimal")
 			}
@@ -532,7 +534,7 @@ func TestSelect(t *testing.T) {
 		t.Fatalf("Failed to prepare test decimal: %s", err)
 	}
 
-	ins := NewInsertRequest(space).Tuple([]interface{}{NewDecimal(number)})
+	ins := NewInsertRequest(space).Tuple([]interface{}{MakeDecimal(number)})
 	resp, err := conn.Do(ins).Get()
 	if err != nil {
 		t.Fatalf("Decimal insert failed: %s", err)
@@ -549,7 +551,7 @@ func TestSelect(t *testing.T) {
 		Offset(offset).
 		Limit(limit).
 		Iterator(IterEq).
-		Key([]interface{}{NewDecimal(number)})
+		Key([]interface{}{MakeDecimal(number)})
 	resp, err = conn.Do(sel).Get()
 	if err != nil {
 		t.Fatalf("Decimal select failed: %s", err.Error())
@@ -559,7 +561,7 @@ func TestSelect(t *testing.T) {
 	}
 	tupleValueIsDecimal(t, resp.Data, number)
 
-	del := NewDeleteRequest(space).Index(index).Key([]interface{}{NewDecimal(number)})
+	del := NewDeleteRequest(space).Index(index).Key([]interface{}{MakeDecimal(number)})
 	resp, err = conn.Do(del).Get()
 	if err != nil {
 		t.Fatalf("Decimal delete failed: %s", err)
@@ -604,7 +606,7 @@ func assertInsert(t *testing.T, conn *Connection, numString string) {
 		t.Fatalf("Failed to prepare test decimal: %s", err)
 	}
 
-	ins := NewInsertRequest(space).Tuple([]interface{}{NewDecimal(number)})
+	ins := NewInsertRequest(space).Tuple([]interface{}{MakeDecimal(number)})
 	resp, err := conn.Do(ins).Get()
 	if err != nil {
 		t.Fatalf("Decimal insert failed: %s", err)
@@ -614,7 +616,7 @@ func assertInsert(t *testing.T, conn *Connection, numString string) {
 	}
 	tupleValueIsDecimal(t, resp.Data, number)
 
-	del := NewDeleteRequest(space).Index(index).Key([]interface{}{NewDecimal(number)})
+	del := NewDeleteRequest(space).Index(index).Key([]interface{}{MakeDecimal(number)})
 	resp, err = conn.Do(del).Get()
 	if err != nil {
 		t.Fatalf("Decimal delete failed: %s", err)
@@ -648,7 +650,7 @@ func TestReplace(t *testing.T) {
 		t.Fatalf("Failed to prepare test decimal: %s", err)
 	}
 
-	rep := NewReplaceRequest(space).Tuple([]interface{}{NewDecimal(number)})
+	rep := NewReplaceRequest(space).Tuple([]interface{}{MakeDecimal(number)})
 	respRep, errRep := conn.Do(rep).Get()
 	if errRep != nil {
 		t.Fatalf("Decimal replace failed: %s", errRep)
@@ -662,7 +664,7 @@ func TestReplace(t *testing.T) {
 		Index(index).
 		Limit(1).
 		Iterator(IterEq).
-		Key([]interface{}{NewDecimal(number)})
+		Key([]interface{}{MakeDecimal(number)})
 	respSel, errSel := conn.Do(sel).Get()
 	if errSel != nil {
 		t.Fatalf("Decimal select failed: %s", errSel)

decimal/example_test.go

@@ -35,7 +35,7 @@ func Example() {
 
 	spaceNo := uint32(524)
 
-	number, err := NewDecimalFromString("-22.804")
+	number, err := MakeDecimalFromString("-22.804")
 	if err != nil {
 		log.Fatalf("Failed to prepare test decimal: %s", err)
 	}