Fix side-effects of checking type of argument

Author: edif2008

internals/cli/argument.go

@@ -14,6 +14,7 @@ type Argument struct {
 }
 
 type ArgValue interface {
+	String() string
 	Set(string) error
 }
 
@@ -46,30 +47,49 @@ func (s *StringValue) Set(replacer string) error {
 	return nil
 }
 
+func (s *StringValue) String() string {
+	return s.Value
+}
+
 type StringListValue []string
 
 func (s *StringListValue) Set(replacer string) error {
 	*s = append(*s, replacer)
 	return nil
 }
 
+func (s *StringListValue) String() string {
+	return "StringListValue"
+}
+
 type URLValue struct {
 	*url.URL
 }
 
-func (s *URLValue) Set(replacer string) error {
+func (s URLValue) Set(replacer string) error {
 	var err error
 	s.URL, err = url.Parse(replacer)
 	return err
 }
 
+func (s *URLValue) String() string {
+	if s.URL == nil  {
+		return ""
+	}
+	return s.URL.String()
+}
+
 type ByteValue []byte
 
 func (s *ByteValue) Set(replacer string) error {
 	*s = []byte(replacer)
 	return nil
 }
 
+func (s *ByteValue) String() string {
+	return string(*s)
+}
+
 func getRequired(params []Argument) int {
 	required := 0
 	for _, arg := range params {

internals/cli/error_handler.go

@@ -2,8 +2,6 @@ package cli
 
 import (
 	"fmt"
-	"reflect"
-	"strings"
 )
 
 func (c *CommandClause) argumentError(args []string) error {
@@ -12,7 +10,7 @@ func (c *CommandClause) argumentError(args []string) error {
 	}
 	errorText, minimum, maximum := "", getRequired(c.Args), len(c.Args)
 
-	if strings.Contains(reflect.TypeOf(c.Args[0].Value).String(), "List") {
+	if c.Args[0].Value.String() == new(StringListValue).String() {
 		errorText += fmt.Sprintf(`"%s" requires at least %d %s.`, c.fullCommand(), minimum, pluralize("argument", minimum))
 	} else if minimum == maximum {
 		errorText += fmt.Sprintf(`"%s" requires exactly %d %s.`, c.fullCommand(), minimum, pluralize("argument", minimum))