Forward Declaration - Forward Reference

The term forward reference is sometimes used as a synonym of forward declaration. However, more often it is taken to refer to the actual use of an entity before any declaration; that is, the first reference to second in the code above is a forward reference. Thus, we may say that because forward declarations are mandatory in Pascal, forward references are prohibited.

An example of (valid) forward reference in C++:

class C { public: void mutator(int x) { myValue = x; } int accessor { return myValue; } private: int myValue; };

In this example, there are two references to myValue before it is declared. C++ generally prohibits forward references, but they are allowed in the special case of class members. Since the member function accessor cannot be compiled until the compiler knows the type of the member variable myValue, it is the compiler's responsibility to remember the definition of accessor until it sees myValue's declaration.

Permitting forward references can greatly increase the complexity and memory requirements of a compiler, and generally prevents the compiler from being implemented in one pass.

Read more about this topic:  Forward Declaration

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Famous quotes containing the word reference:

    I am more and more convinced that, with reference to any public question, it is more important to know what the country thinks of it than what the city thinks. The city does not think much.
    Henry David Thoreau (1817–1862)

    These roses under my window make no reference to former roses or to better ones; they are for what they are; they exist with God to-day. There is no time to them. There is simply the rose; it is perfect in every moment of its existence.
    Ralph Waldo Emerson (1803–1882)