# NSMethodSignature A record of the type information for the return value and parameters of a method. ``` @interface NSMethodSignature : NSObject ``` ## Overview Use an [`NSMethodSignature`](/documentation/Foundation/NSMethodSignature) object to forward messages that the receiving object does not respond to—most notably in the case of distributed objects. You typically create an [`NSMethodSignature`](/documentation/Foundation/NSMethodSignature) object using the instance method (in macOS 10.5 and later you can also use [`signatureWithObjCTypes:`](/documentation/Foundation/NSMethodSignature/signatureWithObjCTypes:)). It is then used to create an [`NSInvocation`](/documentation/Foundation/NSInvocation) object, which is passed as the argument to a message to send the invocation on to whatever other object can handle the message. In the default case, invokes , which raises an exception. For distributed objects, the [`NSInvocation`](/documentation/Foundation/NSInvocation) object is encoded using the information in the [`NSMethodSignature`](/documentation/Foundation/NSMethodSignature) object and sent to the real object represented by the receiver of the message. ### Type Encodings An `NSMethodSignature` object is initialized with an array of characters representing the string encoding of return and argument types for a method. You can get the string encoding of a particular type using the `@encode()` compiler directive. Because string encodings are implementation-specific, you should not hard-code these values. A method signature consists of one or more characters for the method return type, followed by the string encodings of the implicit arguments `self` and `_cmd`, followed by zero or more explicit arguments. You can determine the string encoding and the length of a return type using [`methodReturnType`](/documentation/Foundation/NSMethodSignature/methodReturnType) and [`methodReturnLength`](/documentation/Foundation/NSMethodSignature/methodReturnLength) properties. You can access arguments individually using the [`getArgumentTypeAtIndex:`](/documentation/Foundation/NSMethodSignature/getArgumentTypeAtIndex:) method and [`numberOfArguments`](/documentation/Foundation/NSMethodSignature/numberOfArguments) property. For example, the `NSString` instance method [`contains(_:)`](/documentation/Foundation/NSString/contains(_:)) has a method signature with the following arguments: 1. `@encode(BOOL)` (`c`) for the return type 2. `@encode(id)` (`@`) for the receiver (`self`) 3. `@encode(SEL)` (`:`) for the selector (`_cmd`) 4. `@encode(NSString *)` (`@`) for the first explicit argument See [Type Encodings](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html#//apple_ref/doc/uid/TP40008048-CH100) in [Objective-C Runtime Programming Guide](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Introduction/Introduction.html#//apple_ref/doc/uid/TP40008048) for more information. ## Topics ### Creating a Method Signature Object [`signatureWithObjCTypes:`](/documentation/Foundation/NSMethodSignature/signatureWithObjCTypes:) Returns an `NSMethodSignature` object for the given Objective-C method type string. ### Getting Information on Argument Types [`getArgumentTypeAtIndex:`](/documentation/Foundation/NSMethodSignature/getArgumentTypeAtIndex:) Returns the type encoding for the argument at a given index. [`numberOfArguments`](/documentation/Foundation/NSMethodSignature/numberOfArguments) The number of arguments recorded in the receiver. [`frameLength`](/documentation/Foundation/NSMethodSignature/frameLength) The number of bytes that the arguments, taken together, occupy on the stack. ### Getting Information on Return Types [`methodReturnType`](/documentation/Foundation/NSMethodSignature/methodReturnType) A C string encoding the return type of the method in Objective-C type encoding. [`methodReturnLength`](/documentation/Foundation/NSMethodSignature/methodReturnLength) The number of bytes required for the return value. ### Determining Synchronous Status [`isOneway`](/documentation/Foundation/NSMethodSignature/isOneway) Whether the receiver is asynchronous when invoked through distributed objects. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)