Funktiopesäytymistä

Funktiopesäytymistä, also known as function nesting or nested functions, is a programming concept where a function is defined inside another function. The inner function, or the "nested function," has access to the local variables and parameters of the outer function, even after the outer function has completed its execution. This creates a closure, which is a data structure that captures variables from its surrounding scope.

This technique is useful for creating private helper functions that are only meant to be used within the scope of the outer function. It can also be used to implement advanced programming patterns like decorators or factory functions. In languages that support first-class functions, nested functions can be returned as values, allowing for more dynamic and flexible code design.

The primary advantage of funktiopesäytymistä is encapsulation and data hiding. By keeping helper functions internal, the outer function's interface remains clean and focused on its main purpose. It also helps to avoid polluting the global namespace with auxiliary functions that might not be needed elsewhere. However, excessive nesting can sometimes make code harder to read and debug, so it's important to use this feature judiciously. The specific implementation and capabilities of nested functions can vary between programming languages.