use errUnableToCast error instead of fmt.Errorf

caste.go

@@ -7,6 +7,7 @@ package cast
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"html/template"
 	"reflect"
@@ -15,6 +16,11 @@ import (
 	"time"
 )
 
+var (
+	errNegativeNotAllowed = errors.New("unable to cast negative value")
+	errUnableToCast       = errors.New("unable to cast")
+)
+
 // ToTimeE casts an interface to a time.Time type.
 func ToTimeE(i interface{}) (tim time.Time, err error) {
 	i = indirect(i)
@@ -37,7 +43,7 @@ func ToTimeE(i interface{}) (tim time.Time, err error) {
 	case uint32:
 		return time.Unix(int64(v), 0), nil
 	default:
-		return time.Time{}, newError("unable to cast %#v of type %T to Time", i, i)
+		return time.Time{}, errUnableToCast
 	}
 }
 
@@ -62,7 +68,7 @@ func ToDurationE(i interface{}) (d time.Duration, err error) {
 		}
 		return
 	default:
-		err = newError("unable to cast %#v of type %T to Duration", i, i)
+		err = errUnableToCast
 		return
 	}
 }
@@ -84,7 +90,7 @@ func ToBoolE(i interface{}) (bool, error) {
 	case string:
 		return strconv.ParseBool(i.(string))
 	default:
-		return false, newError("unable to cast %#v of type %T to bool", i, i)
+		return false, errUnableToCast
 	}
 }
 
@@ -122,14 +128,14 @@ func ToFloat64E(i interface{}) (float64, error) {
 		if err == nil {
 			return v, nil
 		}
-		return 0, newError("unable to cast %#v of type %T to float64", i, i)
+		return 0, errUnableToCast
 	case bool:
 		if s {
 			return 1, nil
 		}
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to float64", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -167,14 +173,14 @@ func ToFloat32E(i interface{}) (float32, error) {
 		if err == nil {
 			return float32(v), nil
 		}
-		return 0, newError("unable to cast %#v of type %T to float32", i, i)
+		return 0, errUnableToCast
 	case bool:
 		if s {
 			return 1, nil
 		}
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to float32", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -212,7 +218,7 @@ func ToInt64E(i interface{}) (int64, error) {
 		if err == nil {
 			return v, nil
 		}
-		return 0, newError("unable to cast %#v of type %T to int64", i, i)
+		return 0, errUnableToCast
 	case bool:
 		if s {
 			return 1, nil
@@ -221,7 +227,7 @@ func ToInt64E(i interface{}) (int64, error) {
 	case nil:
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to int64", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -259,7 +265,7 @@ func ToInt32E(i interface{}) (int32, error) {
 		if err == nil {
 			return int32(v), nil
 		}
-		return 0, newError("unable to cast %#v of type %T to int32", i, i)
+		return 0, errUnableToCast
 	case bool:
 		if s {
 			return 1, nil
@@ -268,7 +274,7 @@ func ToInt32E(i interface{}) (int32, error) {
 	case nil:
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to int32", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -306,7 +312,7 @@ func ToInt16E(i interface{}) (int16, error) {
 		if err == nil {
 			return int16(v), nil
 		}
-		return 0, newError("unable to cast %#v of type %T to int16", i, i)
+		return 0, errUnableToCast
 	case bool:
 		if s {
 			return 1, nil
@@ -315,7 +321,7 @@ func ToInt16E(i interface{}) (int16, error) {
 	case nil:
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to int16", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -353,7 +359,7 @@ func ToInt8E(i interface{}) (int8, error) {
 		if err == nil {
 			return int8(v), nil
 		}
-		return 0, newError("unable to cast %#v of type %T to int8", i, i)
+		return 0, errUnableToCast
 	case bool:
 		if s {
 			return 1, nil
@@ -362,7 +368,7 @@ func ToInt8E(i interface{}) (int8, error) {
 	case nil:
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to int8", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -400,7 +406,7 @@ func ToIntE(i interface{}) (int, error) {
 		if err == nil {
 			return int(v), nil
 		}
-		return 0, newError("unable to cast %#v of type %T to int", i, i)
+		return 0, errUnableToCast
 	case bool:
 		if s {
 			return 1, nil
@@ -409,7 +415,7 @@ func ToIntE(i interface{}) (int, error) {
 	case nil:
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to int", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -423,7 +429,7 @@ func ToUintE(i interface{}) (uint, error) {
 		if err == nil {
 			return uint(v), nil
 		}
-		return 0, newError("unable to cast %#v to uint: %s", i, err)
+		return 0, errUnableToCast
 	case int:
 		if s < 0 {
 			return 0, errNegativeNotAllowed
@@ -477,7 +483,7 @@ func ToUintE(i interface{}) (uint, error) {
 	case nil:
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to uint", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -491,7 +497,7 @@ func ToUint64E(i interface{}) (uint64, error) {
 		if err == nil {
 			return v, nil
 		}
-		return 0, newError("unable to cast %#v to uint64: %s", i, err)
+		return 0, errUnableToCast
 	case int:
 		if s < 0 {
 			return 0, errNegativeNotAllowed
@@ -545,7 +551,7 @@ func ToUint64E(i interface{}) (uint64, error) {
 	case nil:
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to uint64", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -559,7 +565,7 @@ func ToUint32E(i interface{}) (uint32, error) {
 		if err == nil {
 			return uint32(v), nil
 		}
-		return 0, newError("unable to cast %#v to uint32: %s", i, err)
+		return 0, errUnableToCast
 	case int:
 		if s < 0 {
 			return 0, errNegativeNotAllowed
@@ -613,7 +619,7 @@ func ToUint32E(i interface{}) (uint32, error) {
 	case nil:
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to uint32", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -627,7 +633,7 @@ func ToUint16E(i interface{}) (uint16, error) {
 		if err == nil {
 			return uint16(v), nil
 		}
-		return 0, newError("unable to cast %#v to uint16: %s", i, err)
+		return 0, errUnableToCast
 	case int:
 		if s < 0 {
 			return 0, errNegativeNotAllowed
@@ -681,7 +687,7 @@ func ToUint16E(i interface{}) (uint16, error) {
 	case nil:
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to uint16", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -695,7 +701,7 @@ func ToUint8E(i interface{}) (uint8, error) {
 		if err == nil {
 			return uint8(v), nil
 		}
-		return 0, newError("unable to cast %#v to uint8: %s", i, err)
+		return 0, errUnableToCast
 	case int:
 		if s < 0 {
 			return 0, errNegativeNotAllowed
@@ -749,7 +755,7 @@ func ToUint8E(i interface{}) (uint8, error) {
 	case nil:
 		return 0, nil
 	default:
-		return 0, newError("unable to cast %#v of type %T to uint8", i, i)
+		return 0, errUnableToCast
 	}
 }
 
@@ -844,7 +850,7 @@ func ToStringE(i interface{}) (string, error) {
 	case error:
 		return s.Error(), nil
 	default:
-		return "", newError("unable to cast %#v of type %T to string", i, i)
+		return "", errUnableToCast
 	}
 }
 
@@ -874,7 +880,7 @@ func ToStringMapStringE(i interface{}) (map[string]string, error) {
 		err := jsonStringToObject(v, &m)
 		return m, err
 	default:
-		return m, newError("unable to cast %#v of type %T to map[string]string", i, i)
+		return m, errUnableToCast
 	}
 }
 
@@ -925,11 +931,11 @@ func ToStringMapStringSliceE(i interface{}) (map[string][]string, error) {
 		for k, val := range v {
 			key, err := ToStringE(k)
 			if err != nil {
-				return m, newError("unable to cast %#v of type %T to map[string][]string", i, i)
+				return m, errUnableToCast
 			}
 			value, err := ToStringSliceE(val)
 			if err != nil {
-				return m, newError("unable to cast %#v of type %T to map[string][]string", i, i)
+				return m, errUnableToCast
 			}
 			m[key] = value
 		}
@@ -937,7 +943,7 @@ func ToStringMapStringSliceE(i interface{}) (map[string][]string, error) {
 		err := jsonStringToObject(v, &m)
 		return m, err
 	default:
-		return m, newError("unable to cast %#v of type %T to map[string][]string", i, i)
+		return m, errUnableToCast
 	}
 	return m, nil
 }
@@ -963,7 +969,7 @@ func ToStringMapBoolE(i interface{}) (map[string]bool, error) {
 		err := jsonStringToObject(v, &m)
 		return m, err
 	default:
-		return m, newError("unable to cast %#v of type %T to map[string]bool", i, i)
+		return m, errUnableToCast
 	}
 }
 
@@ -983,7 +989,7 @@ func ToStringMapE(i interface{}) (map[string]interface{}, error) {
 		err := jsonStringToObject(v, &m)
 		return m, err
 	default:
-		return m, newError("unable to cast %#v of type %T to map[string]interface{}", i, i)
+		return m, errUnableToCast
 	}
 }
 
@@ -1000,14 +1006,14 @@ func ToSliceE(i interface{}) ([]interface{}, error) {
 		}
 		return s, nil
 	default:
-		return s, newError("unable to cast %#v of type %T to []interface{}", i, i)
+		return s, errUnableToCast
 	}
 }
 
 // ToBoolSliceE casts an interface to a []bool type.
 func ToBoolSliceE(i interface{}) ([]bool, error) {
 	if i == nil {
-		return []bool{}, newError("unable to cast %#v of type %T to []bool", i, i)
+		return []bool{}, errUnableToCast
 	}
 
 	switch v := i.(type) {
@@ -1023,13 +1029,13 @@ func ToBoolSliceE(i interface{}) ([]bool, error) {
 		for j := 0; j < s.Len(); j++ {
 			val, err := ToBoolE(s.Index(j).Interface())
 			if err != nil {
-				return []bool{}, newError("unable to cast %#v of type %T to []bool", i, i)
+				return []bool{}, errUnableToCast
 			}
 			a[j] = val
 		}
 		return a, nil
 	default:
-		return []bool{}, newError("unable to cast %#v of type %T to []bool", i, i)
+		return []bool{}, errUnableToCast
 	}
 }
 
@@ -1050,18 +1056,18 @@ func ToStringSliceE(i interface{}) ([]string, error) {
 	case interface{}:
 		str, err := ToStringE(v)
 		if err != nil {
-			return a, newError("unable to cast %#v of type %T to []string", i, i)
+			return a, errUnableToCast
 		}
 		return []string{str}, nil
 	default:
-		return a, newError("unable to cast %#v of type %T to []string", i, i)
+		return a, errUnableToCast
 	}
 }
 
 // ToIntSliceE casts an interface to a []int type.
 func ToIntSliceE(i interface{}) ([]int, error) {
 	if i == nil {
-		return []int{}, newError("unable to cast %#v of type %T to []int", i, i)
+		return []int{}, errUnableToCast
 	}
 
 	switch v := i.(type) {
@@ -1077,20 +1083,20 @@ func ToIntSliceE(i interface{}) ([]int, error) {
 		for j := 0; j < s.Len(); j++ {
 			val, err := ToIntE(s.Index(j).Interface())
 			if err != nil {
-				return []int{}, newError("unable to cast %#v of type %T to []int", i, i)
+				return []int{}, errUnableToCast
 			}
 			a[j] = val
 		}
 		return a, nil
 	default:
-		return []int{}, newError("unable to cast %#v of type %T to []int", i, i)
+		return []int{}, errUnableToCast
 	}
 }
 
 // ToDurationSliceE casts an interface to a []time.Duration type.
 func ToDurationSliceE(i interface{}) ([]time.Duration, error) {
 	if i == nil {
-		return []time.Duration{}, newError("unable to cast %#v of type %T to []time.Duration", i, i)
+		return []time.Duration{}, errUnableToCast
 	}
 
 	switch v := i.(type) {
@@ -1106,13 +1112,13 @@ func ToDurationSliceE(i interface{}) ([]time.Duration, error) {
 		for j := 0; j < s.Len(); j++ {
 			val, err := ToDurationE(s.Index(j).Interface())
 			if err != nil {
-				return []time.Duration{}, newError("unable to cast %#v of type %T to []time.Duration", i, i)
+				return []time.Duration{}, errUnableToCast
 			}
 			a[j] = val
 		}
 		return a, nil
 	default:
-		return []time.Duration{}, newError("unable to cast %#v of type %T to []time.Duration", i, i)
+		return []time.Duration{}, errUnableToCast
 	}
 }
 
@@ -1152,7 +1158,7 @@ func parseDateWith(s string, dates []string) (d time.Time, e error) {
 			return
 		}
 	}
-	return d, newError("unable to parse date: %s", s)
+	return d, errUnableToCast
 }
 
 // jsonStringToObject attempts to unmarshall a string as JSON into

errors.go

@@ -1,30 +0,0 @@
-package cast
-
-import (
-	"errors"
-	"fmt"
-	"sync"
-)
-
-var errNegativeNotAllowed = errors.New("unable to cast negative value")
-
-type lazyError struct {
-	format string
-	args   []interface{}
-	once   sync.Once
-	result string
-}
-
-func (e *lazyError) Error() string {
-	e.once.Do(func() {
-		e.result = fmt.Sprintf(e.format, e.args...)
-	})
-	return e.result
-}
-
-func newError(format string, args ...interface{}) error {
-	return &lazyError{
-		format: format,
-		args:   args,
-	}
-}

errors_test.go

@@ -1,13 +0,0 @@
-package cast
-
-import (
-	"github.com/stretchr/testify/assert"
-	"testing"
-)
-
-func TestLazyError_Error(t *testing.T) {
-	err := newError("foo")
-
-	assert.NotNil(t, err)
-	assert.Equal(t, err.Error(), "foo")
-}