simplify boilerplate

.gitignore

@@ -4,6 +4,7 @@
 *.dll
 *.so
 *.dylib
+.vscode
 
 # Test binary, build with `go test -c`
 *.test

README.md

@@ -24,19 +24,15 @@ func (i CustomID) MarshalJSON() ([]byte, error) {
 }
 
 func (i *CustomID) UnmarshalJSON(b []byte) error {
-	val, err := null.UnmarshalInt(b)
-	*i = CustomID(val)
-	return err
+	return null.UnmarshalInt(b, (*null.Int)(i))
 }
 
 func (i CustomID) Value() (driver.Value, error) {
 	return null.Int(i).Value()
 }
 
 func (i *CustomID) Scan(value interface{}) error {
-	val, err := null.ScanInt(value)
-	*i = CustomID(val)
-	return err
+	return null.ScanInt(value, (*null.Int)(i))
 }
 ```
 
@@ -54,19 +50,15 @@ func (s CustomString) MarshalJSON() ([]byte, error) {
 }
 
 func (s *CustomString) UnmarshalJSON(b []byte) error {
-	val, err := null.UnmarshalString(b)
-	*s = CustomString(val)
-	return err
+	return null.UnmarshalString(b, (*null.String)(s))
 }
 
 func (s CustomString) Value() (driver.Value, error) {
 	return null.String(s).Value()
 }
 
 func (s *CustomString) Scan(value interface{}) error {
-	val, err := null.ScanString(value)
-	*s = CustomString(val)
-	return err
+	return null.ScanString(value, (*null.String)(s))
 }
 ```
 

null.go

@@ -15,29 +15,32 @@ const NullInt = Int(0)
 
 // UnmarshalInt is a utility method that can be used to unmarshal a json value to an Int and error
 // In the case of an error, null or "" values, NullInt is returned
-func UnmarshalInt(b []byte) (Int, error) {
-	var val *int64
+func UnmarshalInt(b []byte, v *Int) error {
+	val := int64(0)
 	err := json.Unmarshal(b, &val)
-	if err != nil || val == nil {
-		return NullInt, err
+	if err != nil {
+		return err
 	}
-	return Int(*val), nil
+	*v = Int(val)
+	return nil
 }
 
 // ScanInt is a utility method that can be used to scan a db value and return an Int and error
 // In the case of an error, null or "" values, NullInt is returned
-func ScanInt(value interface{}) (Int, error) {
+func ScanInt(value interface{}, v *Int) error {
 	val := &sql.NullInt64{}
 	err := val.Scan(value)
 	if err != nil {
-		return NullInt, err
+		return err
 	}
 
 	if !val.Valid {
-		return NullInt, nil
+		*v = NullInt
+		return nil
 	}
 
-	return Int(val.Int64), nil
+	*v = Int(val.Int64)
+	return nil
 }
 
 // MarshalJSON marshals our int to JSON. 0 values will be marshalled as null
@@ -50,16 +53,12 @@ func (i Int) MarshalJSON() ([]byte, error) {
 
 // UnmarshalJSON unmarshals our JSON to int. null values will be marshalled to 0
 func (i *Int) UnmarshalJSON(b []byte) error {
-	val, err := UnmarshalInt(b)
-	*i = val
-	return err
+	return UnmarshalInt(b, i)
 }
 
 // Scan implements the Scanner interface for Int
 func (i *Int) Scan(value interface{}) error {
-	val, err := ScanInt(value)
-	*i = val
-	return err
+	return ScanInt(value, i)
 }
 
 // Value implements the driver Valuer interface for Int
@@ -79,33 +78,37 @@ const NullString = String("")
 
 // UnmarshalString is a utility method that can be used to unmarshal a json value to a String and error
 // In the case of an error, null or "" values, NullString is returned
-func UnmarshalString(b []byte) (String, error) {
+func UnmarshalString(b []byte, v *String) error {
 	var val *string
 	err := json.Unmarshal(b, &val)
 	if err != nil {
-		return NullString, err
+		return err
 	}
 	if val == nil {
-		return NullString, nil
+		*v = NullString
+		return nil
 	}
 
-	return String(*val), nil
+	*v = String(*val)
+	return nil
 }
 
 // ScanString is a utility method that can be used to scan a db value and return a String and error
 // In the case of an error, null or "" values, NullString is returned
-func ScanString(value interface{}) (String, error) {
+func ScanString(value interface{}, v *String) error {
 	val := &sql.NullString{}
 	err := val.Scan(value)
 	if err != nil {
-		return NullString, err
+		return err
 	}
 
 	if !val.Valid {
-		return NullString, nil
+		*v = NullString
+		return nil
 	}
 
-	return String(val.String), nil
+	*v = String(val.String)
+	return nil
 }
 
 // MarshalJSON marshals our string to JSON. "" values will be marshalled as null
@@ -118,16 +121,12 @@ func (s String) MarshalJSON() ([]byte, error) {
 
 // UnmarshalJSON unmarshals our json to a string. null values will be marshalled to ""
 func (s *String) UnmarshalJSON(b []byte) error {
-	val, err := UnmarshalString(b)
-	*s = val
-	return err
+	return UnmarshalString(b, s)
 }
 
 // Scan implements the Scanner interface for String
 func (s *String) Scan(value interface{}) error {
-	val, err := ScanString(value)
-	*s = val
-	return err
+	return ScanString(value, s)
 }
 
 // Value implements the driver Valuer interface for String

null_test.go

@@ -18,19 +18,15 @@ func (i CustomID) MarshalJSON() ([]byte, error) {
 }
 
 func (i *CustomID) UnmarshalJSON(b []byte) error {
-	val, err := UnmarshalInt(b)
-	*i = CustomID(val)
-	return err
+	return UnmarshalInt(b, (*Int)(i))
 }
 
 func (i CustomID) Value() (driver.Value, error) {
 	return Int(i).Value()
 }
 
 func (i *CustomID) Scan(value interface{}) error {
-	val, err := ScanInt(value)
-	*i = CustomID(val)
-	return err
+	return ScanInt(value, (*Int)(i))
 }
 
 type OtherCustom = Int
@@ -70,8 +66,8 @@ func TestCustomInt(t *testing.T) {
 		id := CustomID(10)
 		err = json.Unmarshal(b, &id)
 		assert.NoError(t, err)
-		assert.True(t, tc.Value == id)
-		assert.True(t, tc.Test == id)
+		assert.True(t, tc.Value == id, "%d: %s not equal to %s", i, tc.Value, id)
+		assert.True(t, tc.Test == id, "%d: %s not equal to %s", i, tc.Test, id)
 
 		_, err = db.Exec(`INSERT INTO custom_id(id) VALUES($1)`, tc.Value)
 		assert.NoError(t, err)
@@ -168,19 +164,15 @@ func (s CustomString) MarshalJSON() ([]byte, error) {
 }
 
 func (s *CustomString) UnmarshalJSON(b []byte) error {
-	val, err := UnmarshalString(b)
-	*s = CustomString(val)
-	return err
+	return UnmarshalString(b, (*String)(s))
 }
 
 func (s CustomString) Value() (driver.Value, error) {
 	return String(s).Value()
 }
 
 func (s *CustomString) Scan(value interface{}) error {
-	val, err := ScanString(value)
-	*s = CustomString(val)
-	return err
+	return ScanString(value, (*String)(s))
 }
 
 const NullCustomString = CustomString("")
@@ -266,18 +258,18 @@ func TestString(t *testing.T) {
 		{NullString, "null", nil},
 	}
 
-	for _, tc := range tcs {
+	for i, tc := range tcs {
 		_, err = db.Exec(`DELETE FROM custom_string;`)
 		assert.NoError(t, err)
 
 		b, err := json.Marshal(tc.Value)
 		assert.NoError(t, err)
-		assert.True(t, tc.JSON == string(b), "%s not equal to %s", tc.JSON, string(b))
+		assert.True(t, tc.JSON == string(b), "%d: %s not equal to %s", i, tc.JSON, string(b))
 
 		str := String("blah")
 		err = json.Unmarshal(b, &str)
 		assert.NoError(t, err)
-		assert.True(t, tc.Value == str)
+		assert.True(t, tc.Value == str, "%d: %s not equal to %s", i, tc.Value, str)
 
 		_, err = db.Exec(`INSERT INTO custom_string(string) VALUES($1)`, tc.Value)
 		assert.NoError(t, err)