Function

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Functions are the main backbone of programs; they are what make an application actually do something. In many cases, a function takes a set of parameters and "transforms" itself into a set of one or more return values. However, neither a parameter set nor a return value are required in some languages.

Generally, functions are recognized by a name followed by parenthesis, such as main(), but this is language-dependent. In pseudocode, a function to calculate distance between two points might look like:

distance(x1, y1, x2, y2)
{
    dx = x2 - x1;
    dy = y2 - y1;
    return sqrt(dx * dx + dy * dy)
}

A method is another type of function, but it carries a reference to the particular object instance that called it, crucial for object-oriented languages. Keywords that refer to the calling object are commonly this or self. Methods are sometimes called via a different calling syntax than a regular function (for example, Lua uses var.function() for regular calls and var:method() for method calls).

In some languages, functions can be treated as though they were normal variables, allowing for more flexibility in some situations.