Added Unique Tag

README.md

@@ -86,6 +86,9 @@ regexp
 
 nonnil
 	Validates that the given value is not nil. (Usage: nonnil)
+
+unique
+	Validates that the given values of an array or slice are unique. (Usage: unique)
 ```
 
 Custom validators

builtins.go

@@ -287,3 +287,31 @@ func nonnil(v interface{}, param string) error {
 	}
 	return nil
 }
+
+// unique validates uniqueness of elements of an array
+func unique(v interface{}, _ string) error {
+	arr := reflect.ValueOf(v)
+	if arr.Kind() == reflect.Ptr {
+		if arr.IsNil() {
+			return nil
+		}
+		arr = arr.Elem()
+	}
+	switch arr.Kind() {
+	case reflect.Slice, reflect.Array:
+		m := make(map[interface{}]bool)
+		for i := 0; i < arr.Len(); i++ {
+			val := arr.Index(i).Interface()
+			_, exists := m[val]
+			if exists {
+				return ErrRepeating
+			}
+
+			m[val] = true
+		}
+	default:
+		return ErrUnsupported
+	}
+
+	return nil
+}

validator.go

@@ -73,6 +73,8 @@ var (
 	ErrInvalid = TextErr{errors.New("invalid value")}
 	// ErrCannotValidate is the error returned when a struct is unexported
 	ErrCannotValidate = TextErr{errors.New("cannot validate unexported struct")}
+	// ErrRepeating is the error returned when the elements are not unique
+	ErrRepeating = TextErr{errors.New("repeating value found")}
 )
 
 // ErrorMap is a map which contains all errors from validating a struct.
@@ -140,6 +142,7 @@ func NewValidator() *Validator {
 			"max":     max,
 			"regexp":  regex,
 			"nonnil":  nonnil,
+			"unique":  unique,
 		},
 		printJSON: false,
 	}