add NewFromFloat #108 (#116)

README.md

@@ -60,6 +60,10 @@ Initialize Money by using smallest unit value (e.g 100 represents 1 pound). Use
 ```go
 pound := money.New(100, money.GBP)
 ```
+Or initialize Money using the direct amount.
+```go
+quarterEuro := money.NewFromFloat(0.25, money.EUR)
+```
 Comparison
 -
 **Go-money** provides base compare operations like:

money.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"math"
 )
 
 // Injection points for backward compatibility.
@@ -85,6 +86,13 @@ func New(amount int64, code string) *Money {
 	}
 }
 
+// NewFromFloat creates and returns new instance of Money from a float64.
+// Always rounding trailing decimals down.
+func NewFromFloat(amount float64, currency string) *Money {
+	currencyDecimals := math.Pow10(GetCurrency(currency).Fraction)
+	return New(int64(amount*currencyDecimals), currency)
+}
+
 // Currency returns the currency used by Money.
 func (m *Money) Currency() *Currency {
 	return m.currency

money_test.go

@@ -629,6 +629,24 @@ func TestMoney_Amount(t *testing.T) {
 	}
 }
 
+func TestNewFromFloat(t *testing.T) {
+	m := NewFromFloat(12.34, EUR)
+
+	if m.amount != 1234 {
+		t.Errorf("Expected %d got %d", 1234, m.amount)
+	}
+
+	if m.currency.Code != EUR {
+		t.Errorf("Expected currency %s got %s", EUR, m.currency.Code)
+	}
+
+	m = NewFromFloat(-0.125, EUR)
+
+	if m.amount != -12 {
+		t.Errorf("Expected %d got %d", -12, m.amount)
+	}
+}
+
 func TestDefaultMarshal(t *testing.T) {
 	given := New(12345, IQD)
 	expected := `{"amount":12345,"currency":"IQD"}`