Index: src/OFArray.h
==================================================================
--- src/OFArray.h
+++ src/OFArray.h
@@ -13,11 +13,11 @@
 #import "OFDataArray.h"
 
 /**
  * The OFArray class provides a class for storing objects in an array.
  */
-@interface OFArray: OFObject <OFCopying>
+@interface OFArray: OFObject <OFCopying, OFMutableCopying>
 {
 	OFDataArray *array;
 }
 
 /**

Index: src/OFArray.m
==================================================================
--- src/OFArray.m
+++ src/OFArray.m
@@ -52,10 +52,28 @@
 - (id)copy
 {
 	OFArray *new = [OFArray array];
 	OFObject **objs;
 	size_t len, i;
+
+	objs = [array data];
+	len = [array count];
+
+	[new->array addNItems: len
+		   fromCArray: objs];
+
+	for (i = 0; i < len; i++)
+		[objs[i] retain];
+
+	return new;
+}
+
+- (id)mutableCopy
+{
+	OFArray *new = [OFMutableArray array];
+	OFObject **objs;
+	size_t len, i;
 
 	objs = [array data];
 	len = [array count];
 
 	[new->array addNItems: len

Index: src/OFObject.h
==================================================================
--- src/OFObject.h
+++ src/OFObject.h
@@ -220,5 +220,16 @@
 /**
  * \return A copy of the object
  */
 - (id)copy;
 @end
+
+/**
+ * This protocol is implemented by objects that can be mutable and immutable
+ * and allows returning a mutable copy.
+ */
+@protocol OFMutableCopying
+/**
+ * \return A copy of the object
+ */
+- (id)mutableCopy;
+@end

Index: src/OFString.h
==================================================================
--- src/OFString.h
+++ src/OFString.h
@@ -18,11 +18,11 @@
 extern int of_string_check_utf8(const char *str, size_t len);
 
 /**
  * A class for managing strings.
  */
-@interface OFString: OFObject <OFCopying>
+@interface OFString: OFObject <OFCopying, OFMutableCopying>
 {
 	char	     *string;
 #ifdef __objc_INCLUDE_GNU
 	unsigned int length;
 #else

Index: src/OFString.m
==================================================================
--- src/OFString.m
+++ src/OFString.m
@@ -250,10 +250,15 @@
 
 - (id)copy
 {
 	return [OFString stringWithCString: string];
 }
+
+- (id)mutableCopy
+{
+	return [OFMutableString stringWithCString: string];
+}
 
 - (BOOL)isEqual: (id)obj
 {
 	if (![obj isKindOf: [OFString class]])
 		return NO;