In computer science, a type signature or type annotation defines the inputs and outputs for a function, subroutine or method. A type signature includes at least the function name and the number of its arguments. In some programming languages, it may also specify the function's return type, the types of its arguments, or errors it may pass back.
Contents |
In C and C++ the type signature is declared by the most-commonly known function prototype. In C/C++, a function declaration reflects its use; for example, a function pointer that would be invoked as:
char c; double d; int retVal = (*fPtr)(c, d);
has the signature:
int (*fPtr)(char c, double d);
In Erlang, type signatures may be optionally declared, as:
-spec(function_name(type1(), type2(), ...) -> out_type()).
For example:
-spec(is_even(number()) -> boolean()).
A type signature in the Haskell programming language is written, generally, in the following format:
functionName :: arg1Type -> arg2Type -> ... -> argNType
Notice that the type of the result can be regarded as everything past the first supplied argument. This is a consequence of currying, which is made possible by Haskell's support for first-class functions. That is, given a function that takes in two inputs, but had one argument supplied, the function is "curried" to produce a function of one argument—the one that is not supplied. Thus calling f(x), where f :: a -> b -> c, yields a new function f' :: b -> c that can be called f'(b) to produce c.
The actual type specifications can consist of an actual type, such as {{Haskell|Integer, or a general type variable that is used in parametric polymorphic functions, such as a, or b, or anyType. So we can write something like: functionName :: a -> a -> ... -> a
Since Haskell supports higher-order functions, functions can be passed as arguments. This is written as: functionName :: (a -> a) -> a
This function takes in a function with type signature a -> a, and returns data of type a out.
In the Java virtual machine, internal type signatures are used to identify methods and classes at the level of the virtual machine code.
Example: The method String String.substring(int, int) is represented as Ljava/lang/String/substring(II)Ljava/lang/String;.
The signature of a function is a way of describing the parameters and parameter types with which a legal call to the function can be made. It contains the name of the function, its parameters and their type, and the return value. Signatures may also be referred to as "function signatures", "method signatures", or "prototype definitions".
The notion of a function signature is an important concept for all computer science undergraduates
The practice of multiple inheritance requires careful consideration of the function signatures to avoid unpredictable results.
Computer science theory and the teaching of polymorphism in particular makes much use of the concept of function signature.
Roughly equivalent to its prototype definition in the C programming language.
CS, like many sciences, reuses terminology frequently. If you encounter the term 'signature' in an area of CS not concerned with programming then be sure to check your terminology with the published texts to avoid confusion.
Other areas of Computer Science where you might encounter the term signature:
In the ML family of programming languages, signature is a keyword referring to a construct of the module system that plays the role of an interface.
In computer programming, especially object-oriented programming, a method is commonly identified by its unique method signature, which usually includes the method name, and the number, types and order of its parameters.[1] A method signature is the smallest type of a method.
In C/C++, the method signature is the method name and the number and type of its parameters, but it is possible to have a last parameter that consists of an array of values:
int printf(const char*, ...);
Manipulation of these parameters can be done by using the routines in the standard library header <stdarg.h>.
Similar to the C syntax, C# sees as the method signature its name and the number and type of its parameters, where the last parameter may comprise of an array of values:[2]
void Add(out int sum, params int[] value); [...] Add(out sum, 3, 5, 7, 11, -1); // sum == 25
In the Java programming language, a method signature is the method name and the number and type of its parameters. Return types are not considered to be a part of the method signature.
methodName(parameters) {...};
For example, the following two methods have distinct signatures:
doSomething(int y); doSomething(String y);
The following two methods do have the same signatures and are considered the same, as only the return value differs. The name of the parameter is not part of the method signature and is ignored by the compiler for checking method uniqueness.
int doSomething(int y) String doSomething(int x)
In the Objective-C programming language, method signatures for an object are declared in the interface header file. For example,
- (id)initWithInt:(int)value;
defines a method initWithInt that returns a general object (an id) and takes one integer argument. Objective-C only requires a type in a signature to be explicit when the type is not id; this signature is equivalent:
- initWithInt:(int)value;