安全地从 int 型转换为 int8：

    1. func Uint8FromInt(n int) (uint8, error) {
    2.     if 0 <= n && n <= math.MaxUint8 { // conversion is safe
    3.         return uint8(n), nil
    4.     }
    5.     return 0, fmt.Errorf("%d is out of the uint8 range", n)
    6. }

    安全地从 float64 转换为 int：

    1. func IntFromFloat64(x float64) int {
    2.     if math.MinInt32 <= x && x <= math.MaxInt32 { // x lies in the integer range
    3.         whole, fraction := math.Modf(x)
    4.         if fraction >= 0.5 {
    5.             whole++
    6.         }
    7.         return int(whole)
    8.     }
    9.     panic(fmt.Sprintf("%g is out of the int32 range", x))
    10. }