add func Atoi to convert string base 10

README.md

@@ -73,3 +73,5 @@ the code for a complete set.
     cast.ToInt(eight)              // 8
     cast.ToInt(nil)                // 0
 
+    cast.Atoi("0890")              // 890
+

cast.go

@@ -6,7 +6,9 @@
 // Package cast provides easy and safe casting in Go.
 package cast
 
-import "time"
+import (
+	"time"
+)
 
 // ToBool casts an interface to a bool type.
 func ToBool(i interface{}) bool {
@@ -73,6 +75,11 @@ func ToInt(i interface{}) int {
 	return v
 }
 
+func Atoi(i interface{}) int {
+	v, _ := AtoiE(i)
+	return v
+}
+
 // ToUint casts an interface to a uint type.
 func ToUint(i interface{}) uint {
 	v, _ := ToUintE(i)

cast_test.go

@@ -161,6 +161,16 @@ func TestToIntE(t *testing.T) {
 		func(v interface{}) interface{} { return ToInt(v) },
 	)
 }
+func TestAtoiE(t *testing.T) {
+	tests := createNumberTestSteps(int(0), int(1), int(8), int(-8), int(8), int(-8))
+	tests = append(tests, testStep{input: "0890", expect: 890, iserr: false})
+	runNumberTest(
+		qt.New(t),
+		tests,
+		func(v interface{}) (interface{}, error) { return AtoiE(v) },
+		func(v interface{}) interface{} { return Atoi(v) },
+	)
+}
 
 func TestToInt64E(t *testing.T) {
 	tests := createNumberTestSteps(int64(0), int64(1), int64(8), int64(-8), int64(8), int64(-8))

caste.go

@@ -487,6 +487,57 @@ func ToIntE(i interface{}) (int, error) {
 	}
 }
 
+func AtoiE(i interface{}) (int, error) {
+	i = indirect(i)
+
+	intv, ok := toInt(i)
+	if ok {
+		return intv, nil
+	}
+
+	switch s := i.(type) {
+	case int64:
+		return int(s), nil
+	case int32:
+		return int(s), nil
+	case int16:
+		return int(s), nil
+	case int8:
+		return int(s), nil
+	case uint:
+		return int(s), nil
+	case uint64:
+		return int(s), nil
+	case uint32:
+		return int(s), nil
+	case uint16:
+		return int(s), nil
+	case uint8:
+		return int(s), nil
+	case float64:
+		return int(s), nil
+	case float32:
+		return int(s), nil
+	case string:
+		v, err := strconv.ParseInt(trimZeroDecimal(s), 10, 0)
+		if err == nil {
+			return int(v), nil
+		}
+		return 0, fmt.Errorf("unable to cast %#v of type %T to int64", i, i)
+	case json.Number:
+		return ToIntE(string(s))
+	case bool:
+		if s {
+			return 1, nil
+		}
+		return 0, nil
+	case nil:
+		return 0, nil
+	default:
+		return 0, fmt.Errorf("unable to cast %#v of type %T to int", i, i)
+	}
+}
+
 // ToUintE casts an interface to a uint type.
 func ToUintE(i interface{}) (uint, error) {
 	i = indirect(i)