Add, Subtract, Multiply Many

money.go

@@ -198,26 +198,56 @@ func (m *Money) Negative() *Money {
 }
 
 // Add returns new Money struct with value representing sum of Self and Other Money.
-func (m *Money) Add(om *Money) (*Money, error) {
-	if err := m.assertSameCurrency(om); err != nil {
-		return nil, err
+func (m *Money) Add(om ...*Money) (*Money, error) {
+	if len(om) == 0 {
+		panic("At least one Money is required to add")
 	}
 
-	return &Money{amount: mutate.calc.add(m.amount, om.amount), currency: m.currency}, nil
+	k := New(0, m.currency.Code)
+
+	for i := 0; i < len(om); i++ {
+		if err := m.assertSameCurrency(om[i]); err != nil {
+			return nil, err
+		}
+
+		k.amount = mutate.calc.add(k.amount, om[i].amount)
+	}
+
+	return &Money{amount: mutate.calc.add(m.amount, k.amount), currency: m.currency}, nil
 }
 
 // Subtract returns new Money struct with value representing difference of Self and Other Money.
-func (m *Money) Subtract(om *Money) (*Money, error) {
-	if err := m.assertSameCurrency(om); err != nil {
-		return nil, err
+func (m *Money) Subtract(om ...*Money) (*Money, error) {
+	if len(om) == 0 {
+		panic("At least one Money is required to subtract")
 	}
 
-	return &Money{amount: mutate.calc.subtract(m.amount, om.amount), currency: m.currency}, nil
+	k := New(0, m.currency.Code)
+
+	for i := 0; i < len(om); i++ {
+		if err := m.assertSameCurrency(om[i]); err != nil {
+			return nil, err
+		}
+
+		k.amount = mutate.calc.add(k.amount, om[i].amount)
+	}
+
+	return &Money{amount: mutate.calc.subtract(m.amount, k.amount), currency: m.currency}, nil
 }
 
 // Multiply returns new Money struct with value representing Self multiplied value by multiplier.
-func (m *Money) Multiply(mul int64) *Money {
-	return &Money{amount: mutate.calc.multiply(m.amount, mul), currency: m.currency}
+func (m *Money) Multiply(mul ...int64) *Money {
+	if len(mul) == 0 {
+		panic("At least one multiplier is required to multiply")
+	}
+
+	k := New(1, m.currency.Code)
+
+	for i := 0; i < len(mul); i++ {
+		k.amount = mutate.calc.multiply(k.amount, mul[i])
+	}
+
+	return &Money{amount: mutate.calc.multiply(m.amount, k.amount), currency: m.currency}
 }
 
 // Round returns new Money struct with value rounded to nearest zero.

money_test.go

@@ -320,6 +320,36 @@ func TestMoney_Add2(t *testing.T) {
 	}
 }
 
+func TestMoney_Add3(t *testing.T) {
+	tcs := []struct {
+		amount1  int64
+		amount2  int64
+		amount3  int64
+		expected int64
+	}{
+		{5, 5, 3, 13},
+		{10, 5, 4, 19},
+		{1, -1, 2, 2},
+		{3, -1, -4, -2},
+	}
+
+	for _, tc := range tcs {
+		mon1 := New(tc.amount1, EUR)
+		mon2 := New(tc.amount2, EUR)
+		mon3 := New(tc.amount3, EUR)
+		r, err := mon1.Add(mon2, mon3)
+
+		if err != nil {
+			t.Error(err)
+		}
+
+		if r.Amount() != tc.expected {
+			t.Errorf("Expected %d + %d + %d = %d got %d", tc.amount1, tc.amount2, tc.amount3,
+				tc.expected, r.amount)
+		}
+	}
+}
+
 func TestMoney_Subtract(t *testing.T) {
 	tcs := []struct {
 		amount1  int64
@@ -357,6 +387,36 @@ func TestMoney_Subtract2(t *testing.T) {
 	}
 }
 
+func TestMoney_Subtract3(t *testing.T) {
+	tcs := []struct {
+		amount1  int64
+		amount2  int64
+		amount3  int64
+		expected int64
+	}{
+		{5, 5, 3, -3},
+		{10, -5, 4, 11},
+		{1, -1, 2, 0},
+		{7, 1, -4, 10},
+	}
+
+	for _, tc := range tcs {
+		mon1 := New(tc.amount1, EUR)
+		mon2 := New(tc.amount2, EUR)
+		mon3 := New(tc.amount3, EUR)
+		r, err := mon1.Subtract(mon2, mon3)
+
+		if err != nil {
+			t.Error(err)
+		}
+
+		if r.Amount() != tc.expected {
+			t.Errorf("Expected (%d) - (%d) - (%d) = %d got %d", tc.amount1, tc.amount2, tc.amount3,
+				tc.expected, r.amount)
+		}
+	}
+}
+
 func TestMoney_Multiply(t *testing.T) {
 	tcs := []struct {
 		amount     int64
@@ -379,6 +439,29 @@ func TestMoney_Multiply(t *testing.T) {
 	}
 }
 
+func TestMoney_Multiply2(t *testing.T) {
+	tcs := []struct {
+		amount1  int64
+		amount2  int64
+		amount3  int64
+		expected int64
+	}{
+		{5, 5, 5, 125},
+		{10, 5, -3, -150},
+		{1, -1, 6, -6},
+		{1, 0, 2, 0},
+	}
+
+	for _, tc := range tcs {
+		mon1 := New(tc.amount1, EUR)
+		r := mon1.Multiply(tc.amount2, tc.amount3)
+
+		if r.amount != tc.expected {
+			t.Errorf("Expected %d * %d * %d = %d got %d", tc.amount1, tc.amount2, tc.amount3, tc.expected, r.amount)
+		}
+	}
+}
+
 func TestMoney_Round(t *testing.T) {
 	tcs := []struct {
 		amount   int64