This seems like a great opportunity to create a type, which stores the value in a safe and precise integer-based way, but gives you extra behavior you'd want from a decimal type. For instance, a quick implementation might look like this (https://play.golang.org/p/nYbLiadQOc):
// USD represents US dollar amount in terms of cents
type USD int64
// ToUSD converts a float64 to USD
// e.g. 1.23 to $1.23, 1.345 to $1.35
func ToUSD(f float64) USD {
return USD((f * 100) + 0.5)
}
// Float64 converts a USD to float64
func (m USD) Float64() float64 {
x := float64(m)
x = x / 100
return x
}
// Multiply safely multiplies a USD value by a float64, rounding
// to the nearest cent.
func (m USD) Multiply(f float64) USD {
x := (float64(m) * f) + 0.5
return USD(x)
}
// String returns a formatted USD value
func (m USD) String() string {
x := float64(m)
x = x / 100
return fmt.Sprintf("$%.2f", x)
}
The given type behaves the way one might expect, especially given tricky use-cases.
fmt.Println("Product costs $9.09. Tax is 9.75%.")
f := 9.09
t := 0.0975
ft := f * t
fmt.Printf("Floats: %.18f * %.18f = %.18f\n", f, t, ft)
u := ToUSD(9.09)
ut := u.Multiply(t)
fmt.Printf("USD: %v * %v = %v\n", u, t, ut)
Product costs $9.09. Tax is 9.75%.
Floats: 9.089999999999999858 * 0.097500000000000003 = 0.886275000000000035
USD: $9.09 * 0.0975 = $0.89