feat: add Convert

This PR improves the issues @ldemailly had with its implementation

examples_test.go

@@ -186,3 +186,21 @@ func ExampleToUint() {
 	// 42
 	// conversion issue: -1 (int8) is less than 0 (uint): minimum value for this type exceeded
 }
+
+func ExampleConvert() {
+	a := int(42)
+	i, err := safecast.Convert[int32](a)
+	if err != nil {
+		fmt.Println(err)
+	}
+	fmt.Println(i)
+
+	a = int(math.MaxUint32 + 1)
+	_, err = safecast.ToInt32(a)
+	if err != nil {
+		fmt.Println(err)
+	}
+	// Output:
+	// 42
+	// conversion issue: 4294967296 (int) is greater than 2147483647 (int32): maximum value for this type exceeded
+}

generics.go

@@ -0,0 +1,103 @@
+package safecast
+
+import (
+	"math"
+)
+
+func Negative[T Type](t T) bool {
+	return t < 0
+}
+
+func SameSign[T1, T2 Type](a T1, b T2) bool {
+	return Negative(a) == Negative(b)
+}
+
+// idea: @ccoVeille (me)
+// Suggestion of improvement by @ldemailly
+// Fixed floats issues by @ccoveille (me)
+
+func Convert[NumOut Type, NumIn Type](orig NumIn) (converted NumOut, err error) {
+	converted = NumOut(orig)
+
+	if !SameSign(orig, converted) {
+		err = ErrConversionIssue
+		return
+	}
+
+	base := orig
+	switch f := any(orig).(type) {
+	case float64:
+		base = NumIn(math.Trunc(f))
+	case float32:
+		base = NumIn(math.Trunc(float64(f)))
+	}
+
+	if NumIn(converted) == base {
+		return converted, nil
+	}
+
+	errBoundary := ErrExceedMaximumValue
+	boundary := getUpperBoundary(converted)
+	if Negative(orig) {
+		errBoundary = ErrExceedMinimumValue
+		boundary = getLowerBoundary(converted)
+	}
+
+	return converted, Error{
+		value:    orig,
+		err:      errBoundary,
+		boundary: boundary,
+	}
+}
+
+func getUpperBoundary(value any) any {
+	switch value.(type) {
+	case float64:
+		return float64(math.MaxFloat64)
+	case float32:
+		return float32(math.MaxFloat32)
+	case int64:
+		return int64(math.MaxInt64)
+	case int32:
+		return int32(math.MaxInt32)
+	case int16:
+		return int16(math.MaxInt16)
+	case int8:
+		return int8(math.MaxInt8)
+	case int:
+		return int(math.MaxInt)
+	case uint64:
+		return uint64(math.MaxUint64)
+	case uint32:
+		return uint32(math.MaxUint32)
+	case uint16:
+		return uint16(math.MaxUint16)
+	case uint8:
+		return uint8(math.MaxUint8)
+	case uint:
+		return uint(math.MaxUint)
+	}
+
+	return nil
+}
+
+func getLowerBoundary(value any) any {
+	switch value.(type) {
+	case float64:
+		return -math.MaxFloat64
+	case float32:
+		return -math.MaxFloat32
+	case int64:
+		return math.MinInt64
+	case int32:
+		return math.MinInt32
+	case int16:
+		return math.MinInt16
+	case int8:
+		return math.MinInt8
+	case int:
+		return math.MinInt
+	}
+
+	return 0
+}