Index: src/OFArray.h
==================================================================
--- src/OFArray.h
+++ src/OFArray.h
@@ -194,10 +194,41 @@
  * @return The object at the specified index in the array
  */
 - (ObjectType)objectAtIndex: (size_t)index;
 - (ObjectType)objectAtIndexedSubscript: (size_t)index;
 
+/*!
+ * @brief Returns the value for the specified key
+ *
+ * If the key starts with an `@`, the `@` is stripped and
+ * `[super valueForKey:]` is called.
+ * If the key does not start with an `@`, a new array with the value for the
+ * specified key for each object is returned.
+ *
+ * @note Any nil values are replaced with @ref OFNull!
+ *
+ * @param key The key of the value to return
+ * @return The value for the specified key
+ */
+- (nullable id)valueForKey: (OFString*)key;
+
+/*!
+ * @brief Set the value for the specified key
+ *
+ * If the key starts with an `@`, the `@` is stripped and
+ * `[super setValue:forKey:]` is called.
+ * If the key does not start with an `@`, @ref setValue:forKey: is called for
+ * each object.
+ *
+ * @note A @ref OFNull value is translated to nil!
+ *
+ * @param value The value for the specified key
+ * @param key The key of the value to set
+ */
+- (void)setValue: (nullable id)value
+	  forKey: (OFString*)key;
+
 /*!
  * @brief Copies the objects at the specified range to the specified buffer.
  *
  * @param buffer The buffer to copy the objects to
  * @param range The range to copy

Index: src/OFArray.m
==================================================================
--- src/OFArray.m
+++ src/OFArray.m
@@ -25,10 +25,11 @@
 #import "OFArray_subarray.h"
 #import "OFArray_adjacent.h"
 #import "OFString.h"
 #import "OFXMLElement.h"
 #import "OFDataArray.h"
+#import "OFNull.h"
 
 #import "OFEnumerationMutationException.h"
 #import "OFInvalidArgumentException.h"
 #import "OFOutOfRangeException.h"
 
@@ -272,10 +273,39 @@
 
 - (id)objectAtIndexedSubscript: (size_t)index
 {
 	return [self objectAtIndex: index];
 }
+
+- (id)valueForKey: (OFString*)key
+{
+	OFMutableArray *ret = [OFMutableArray arrayWithCapacity: [self count]];
+
+	for (id object in self) {
+		id value = [object valueForKey: key];
+
+		if (value == nil)
+			value = [OFNull null];
+
+		[ret addObject: value];
+	}
+
+	[ret makeImmutable];
+
+	return ret;
+}
+
+- (void)setValue: (id)value
+	  forKey: (OFString*)key
+{
+	if (value == [OFNull null])
+		value = nil;
+
+	for (id object in self)
+		[object setValue: value
+			  forKey: key];
+}
 
 - (size_t)indexOfObject: (id)object
 {
 	size_t i = 0;
 

Index: src/OFKeyValueCoding.h
==================================================================
--- src/OFKeyValueCoding.h
+++ src/OFKeyValueCoding.h
@@ -28,11 +28,11 @@
  * Key Value Coding makes it possible to access properties dynamically using
  * the interface described by this protocol.
  */
 @protocol OFKeyValueCoding
 /*!
- * @brief Return the value for the specified key
+ * @brief Returns the value for the specified key
  *
  * @param key The key of the value to return
  * @return The value for the specified key
  */
 - (nullable id)valueForKey: (OFString*)key;

Index: tests/OFArrayTests.m
==================================================================
--- tests/OFArrayTests.m
+++ tests/OFArrayTests.m
@@ -16,10 +16,12 @@
 
 #include "config.h"
 
 #import "OFArray.h"
 #import "OFString.h"
+#import "OFNumber.h"
+#import "OFURL.h"
 #import "OFAutoreleasePool.h"
 
 #import "OFEnumerationMutationException.h"
 #import "OFOutOfRangeException.h"
 
@@ -293,11 +295,11 @@
 		}
 
 		return nil;
 		}]) && [[m[0] description] isEqual: @"(\n\tfoo,\n\tbar\n)"])
 
-	TEST(@"-[mappedArrayUsingBLock]",
+	TEST(@"-[mappedArrayUsingBlock:]",
 	    [[[m[0] mappedArrayUsingBlock: ^ id (id obj, size_t idx) {
 		switch (idx) {
 		case 0:
 			return @"foobar";
 		case 1:
@@ -318,8 +320,26 @@
 		[left appendString: right];
 		return left;
 	    }])
 #endif
 
+	TEST(@"-[valueForKey:]",
+	    [[[OFArray arrayWithObjects: @"foo", @"bar", @"quxqux", nil]
+	    valueForKey: @"length"] isEqual:
+	    [OFArray arrayWithObjects: [OFNumber numberWithSize: 3],
+	    [OFNumber numberWithSize: 3], [OFNumber numberWithSize: 6], nil]])
+
+	m[0] = [OFMutableArray arrayWithObjects:
+	    [OFURL URLWithString: @"http://foo.bar/"],
+	    [OFURL URLWithString: @"http://bar.qux/"],
+	    [OFURL URLWithString: @"http://qux.quxqux/"], nil];
+	TEST(@"-[setValue:forKey:]",
+	    R([m[0] setValue: [OFNumber numberWithShort: 1234]
+		      forKey: @"port"]) &&
+	    [m[0] isEqual: [OFArray arrayWithObjects:
+	    [OFURL URLWithString: @"http://foo.bar:1234/"],
+	    [OFURL URLWithString: @"http://bar.qux:1234/"],
+	    [OFURL URLWithString: @"http://qux.quxqux:1234/"], nil]])
+
 	[pool drain];
 }
 @end