Index: src/OFMutableArray.h
==================================================================
--- src/OFMutableArray.h
+++ src/OFMutableArray.h
@@ -9,10 +9,14 @@
  * the packaging of this file.
  */
 
 #import "OFArray.h"
 
+#ifdef OF_HAVE_BLOCKS
+typedef id (^of_array_replace_block_t)(id obj, size_t idx, BOOL *stop);
+#endif
+
 /**
  * \brief A class for storing, adding and removing objects in an array.
  */
 @interface OFMutableArray: OFArray
 {
@@ -100,6 +104,15 @@
  * \param nobjects The number of objects to remove
  * \param index The index at which the objects are removed
  */
 - (void)removeNObjects: (size_t)nobjects
 	       atIndex: (size_t)index;
+
+#ifdef OF_HAVE_BLOCKS
+/**
+ * Replaces each object with the object returned by the block.
+ *
+ * \param block The block which returns a new object for each object
+ */
+- (void)replaceObjectsUsingBlock: (of_array_replace_block_t)block;
+#endif
 @end

Index: src/OFMutableArray.m
==================================================================
--- src/OFMutableArray.m
+++ src/OFMutableArray.m
@@ -250,7 +250,31 @@
 			    newWithClass: isa];
 
 		block(objs[i], i, &stop);
 	}
 }
+
+- (void)replaceObjectsUsingBlock: (of_array_replace_block_t)block
+{
+	OFObject **objs = [array cArray];
+	size_t i, count = [array count];
+	BOOL stop = NO;
+	unsigned long mutations2 = mutations;
+
+	for (i = 0; i < count && !stop; i++) {
+		if (mutations != mutations2)
+			@throw [OFEnumerationMutationException
+			    newWithClass: isa];
+
+		id new = block(objs[i], i, &stop);
+
+		if (new == nil)
+			@throw [OFInvalidArgumentException newWithClass: isa
+							       selector: _cmd];
+
+		[new retain];
+		[objs[i] release];
+		objs[i] = new;
+	}
+}
 #endif
 @end

Index: src/OFMutableDictionary.h
==================================================================
--- src/OFMutableDictionary.h
+++ src/OFMutableDictionary.h
@@ -9,10 +9,14 @@
  * the packaging of this file.
  */
 
 #import "OFDictionary.h"
 
+#ifdef OF_HAVE_BLOCKS
+typedef id (^of_dictionary_replace_block_t)(id key, id obj, BOOL *stop);
+#endif
+
 /**
  * \brief A class for using mutable hash tables.
  */
 @interface OFMutableDictionary: OFDictionary
 {
@@ -33,6 +37,15 @@
  * Remove the object with the given key from the dictionary.
  *
  * \param key The key whose object should be removed
  */
 - (void)removeObjectForKey: (OFObject*)key;
+
+#ifdef OF_HAVE_BLOCKS
+/**
+ * Replaces each object with the object returned by the block.
+ *
+ * \param block The block which returns a new object for each object
+ */
+- (void)replaceObjectsUsingBlock: (of_dictionary_replace_block_t)block;
+#endif
 @end

Index: src/OFMutableDictionary.m
==================================================================
--- src/OFMutableDictionary.m
+++ src/OFMutableDictionary.m
@@ -280,7 +280,33 @@
 
 		if (data[i] != NULL && data[i] != DELETED)
 			block(data[i]->key, data[i]->object, &stop);
 	}
 }
+
+- (void)replaceObjectsUsingBlock: (of_dictionary_replace_block_t)block
+{
+	size_t i;
+	BOOL stop = NO;
+	unsigned long mutations2 = mutations;
+
+	for (i = 0; i < size && !stop; i++) {
+		if (mutations != mutations2)
+			@throw [OFEnumerationMutationException
+			    newWithClass: isa];
+
+		if (data[i] != NULL && data[i] != DELETED) {
+			id new = block(data[i]->key, data[i]->object, &stop);
+
+			if (new == nil)
+				@throw [OFInvalidArgumentException
+				    newWithClass: isa
+					selector: _cmd];
+
+			[new retain];
+			[data[i]->object release];
+			data[i]->object = new;
+		}
+	}
+}
 #endif
 @end

Index: tests/OFArrayTests.m
==================================================================
--- tests/OFArrayTests.m
+++ tests/OFArrayTests.m
@@ -220,10 +220,24 @@
 		}
 
 		TEST(@"Detection of mutation during enumeration using blocks",
 		    ok)
 	}
+
+	TEST(@"-[replaceObjectsUsingBlock:]",
+	    R([m[0] replaceObjectsUsingBlock:
+	    ^ id (id obj, size_t idx, BOOL *stop) {
+		switch (idx) {
+		case 0:
+			return @"foo";
+		case 1:
+			return @"bar";
+		}
+
+		return nil;
+	    }]) && [[m[0] objectAtIndex: 0] isEqual: @"foo"] &&
+	    [[m[0] objectAtIndex: 1] isEqual: @"bar"])
 #endif
 
 	[pool drain];
 }
 @end

Index: tests/OFDictionaryTests.m
==================================================================
--- tests/OFDictionaryTests.m
+++ tests/OFDictionaryTests.m
@@ -91,10 +91,22 @@
 	}
 
 	TEST(@"Detection of mutation during Fast Enumeration", ok)
 
 	[dict removeObjectForKey: @""];
+
+	TEST(@"-[replaceObjectsUsingBlock:]",
+	    R([dict replaceObjectsUsingBlock:
+	    ^ id (id key, id obj, BOOL *stop) {
+		if ([key isEqual: keys[0]])
+			return @"value_1";
+		if ([key isEqual: keys[1]])
+			return @"value_2";
+
+		return nil;
+	    }]) && [[dict objectForKey: keys[0]] isEqual: @"value_1"] &&
+	    [[dict objectForKey: keys[1]] isEqual: @"value_2"])
 #endif
 
 #ifdef OF_HAVE_BLOCKS
 	{
 		__block size_t i = 0;