Wrapper function

A wrapper function is a function in a computer program whose main purpose is to call a second function^[1] with little or no additional computation. This is also known as method delegation. Wrapper functions can be used for a number of purposes.

Adapting class/object interfaces

Main article: Adapter pattern

Wrapper functions can be used to adapt an existing class or object to have a different interface. This is especially useful when using existing library code.

Code testing

Wrapper functions can be used to write error checking routines for pre-existing system functions without increasing the length of a code by a large amount by repeating the same error check for each call to the function.^[2] All calls to the original function can be replaced with calls to the wrapper, allowing the programmer to forget about error checking once the wrapper is written.

Multiple inheritance

In a programming language that does not support multiple inheritance of base classes, wrapper functions can be used to simulate it. Below is an example of part of a class that "inherits" from LinkedList and HashSet.

public class StackSet implements Stack, Set {

    private LinkedList stack;
    private HashSet set;

    public boolean push(Object o) {
        if (set.add(o)) then return stack.push(o);
        else return false;
    }

    public Object pop() {
        Object o = stack.pop();
        set.remove(o);
        return o;
    }

    public boolean contains(Object o) {
        return set.contains(o);
    }

}

Programming convenience

Wrapper functions can be used to make writing computer programs easier. An example of this is the MouseAdapter and similar classes in the Java AWT library.^[3]

Library functions and system calls

Many library functions such as in the C Standard Library act as an interface (abstraction) for system calls. For example, "fork" and "execve" are GLIBC functions that call the "fork" and "execve" system calls, respectively.^{[citation needed]}

See also

Adapter pattern

References

1. Reselman, Bob (1998). Using Visual Basic 6. Que. p. 446. ISBN 078971633X, 9780789716330. {{cite book}}: Check |isbn= value: invalid character (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
2. Stevens, Richard (2003). UNIX Network Programming. Addison-Wesley. pp. 5–6, 29. ISBN 0131411551, 9780131411555. {{cite book}}: Check |isbn= value: invalid character (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
3. The Java Tutorials