modify function ToStringE to support type redefinition

cast_test.go

@@ -15,6 +15,23 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+type (
+	intAlias     int
+	int8Alias    int8
+	int16Alias   int16
+	int32Alias   int32
+	int64Alias   int64
+	uintAlias    uint
+	uint8Alias   uint8
+	uint16Alias  uint16
+	uint32Alias  uint32
+	uint64Alias  uint64
+	float32Alias float32
+	float64Alias float64
+	boolAlias    bool
+	stringAlias  string
+)
+
 func TestToUintE(t *testing.T) {
 	tests := []struct {
 		input  interface{}
@@ -605,22 +622,37 @@ func TestToStringE(t *testing.T) {
 		iserr  bool
 	}{
 		{int(8), "8", false},
+		{intAlias(8), "8", false},
 		{int8(8), "8", false},
+		{int8Alias(8), "8", false},
 		{int16(8), "8", false},
+		{int16Alias(8), "8", false},
 		{int32(8), "8", false},
+		{int32Alias(8), "8", false},
 		{int64(8), "8", false},
+		{int64Alias(8), "8", false},
 		{uint(8), "8", false},
+		{uintAlias(8), "8", false},
 		{uint8(8), "8", false},
+		{uint8Alias(8), "8", false},
 		{uint16(8), "8", false},
+		{uint16Alias(8), "8", false},
 		{uint32(8), "8", false},
+		{uint32Alias(8), "8", false},
 		{uint64(8), "8", false},
+		{uint64Alias(8), "8", false},
 		{float32(8.31), "8.31", false},
+		{float32Alias(8.31), "8.31", false},
 		{float64(8.31), "8.31", false},
+		{float64Alias(8.31), "8.31", false},
 		{true, "true", false},
+		{boolAlias(true), "true", false},
 		{false, "false", false},
+		{boolAlias(false), "false", false},
 		{nil, "", false},
 		{[]byte("one time"), "one time", false},
 		{"one more time", "one more time", false},
+		{stringAlias("one more time"), "one more time", false},
 		{template.HTML("one time"), "one time", false},
 		{template.URL("http://somehost.foo"), "http://somehost.foo", false},
 		{template.JS("(1+2)"), "(1+2)", false},

caste.go

@@ -846,9 +846,24 @@ func ToStringE(i interface{}) (string, error) {
 		return s.String(), nil
 	case error:
 		return s.Error(), nil
-	default:
-		return "", fmt.Errorf("unable to cast %#v of type %T to string", i, i)
 	}
+
+	// support type redefinition
+	switch reflect.TypeOf(i).Kind() {
+	case reflect.String:
+		return reflect.ValueOf(i).String(), nil
+	case reflect.Bool:
+		return strconv.FormatBool(reflect.ValueOf(i).Bool()), nil
+	case reflect.Float32:
+		return strconv.FormatFloat(reflect.ValueOf(i).Float(), 'f', -1, 32), nil
+	case reflect.Float64:
+		return strconv.FormatFloat(reflect.ValueOf(i).Float(), 'f', -1, 64), nil
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return strconv.FormatInt(reflect.ValueOf(i).Int(), 10), nil
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		return strconv.FormatUint(reflect.ValueOf(i).Uint(), 10), nil
+	}
+	return "", fmt.Errorf("unable to cast %#v of type %T to string", i, i)
 }
 
 // ToStringMapStringE casts an interface to a map[string]string type.

go.mod

@@ -5,3 +5,5 @@ require (
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/stretchr/testify v1.2.2
 )
+
+go 1.13