requiredargument

A required argument, in programming, is a parameter that must be supplied by the caller when invoking a function or method. If a required argument is not provided, the call is typically considered invalid and will result in an error or exception.

Required arguments are contrasted with optional or defaulted arguments. An optional argument has a default value, so the caller may omit it and the function uses that default. A parameter lacking a default is generally treated as required, though some languages offer mechanisms (such as overloading or keyword-only parameters) to provide alternative ways to supply the needed data.

Enforcement of required arguments varies by language. In statically typed languages, missing required arguments often produces a compile-time error. In dynamically typed languages, the omission usually triggers a run-time error. Some languages support function overloading or named parameters to accommodate different call styles while still requiring certain values.

Examples across common languages illustrate the concept. In Python, a function defined as def f(a, b): pass requires both arguments unless defaults are provided. In JavaScript, function f(a, b) { } can be called with one argument, but missing values may be undefined and lead to runtime checks. In C++, a function declared as void f(int a, int b = 0) makes b optional, while a is required. Ruby and other languages follow similar patterns, emphasizing clear documentation and explicit validation when necessary.

Best practices include documenting which arguments are required, validating inputs early, and providing clear error messages to help callers supply the correct parameters. See also: optional argument, default parameter, argument validation.