Editing Nested function (section)

== Attributes ==

The [[Scope (computer science)|scope]] of a nested function is the block that contains it {{endash}} be it a function block or block within a function body. It is not visible (cannot be called by name) outside its containing block.

A nested function can use [[identifiers]] (i.e. the name of functions, variables, types, classes) declared in any enclosing block, except when they are masked by inner declarations with the same names.

A nested function can be declared within a nested function, recursively, to form a deeply nested structure. 
A deeply nested function can access identifiers declared in all of its enclosing blocks, including enclosing functions.

Nested functions may in certain situations lead to the creation of a [[Closure (computer programming)|closure]]. If it is possible for the nested function to [[Escape analysis|escape]] the enclosing function, for example if functions are [[first class object]]s and a nested function is passed to another function or returned from the enclosing function, then a closure is created and calls to this function can access the environment of the original function. The frame of the immediately enclosing function must continue to be alive until the last referencing closure dies and [[non-local variable|non-local]] [[automatic variable]]s referenced in closures can therefore not be [[stack allocation|stack allocated]] in languages that allow the closure to persist beyond the lifetime of the enclosing block. This is known as the [[funarg problem]] and is a key reason why nested functions was not implemented in some simpler languages as it significantly complicates code generation and analysis, especially when functions are nested to various levels, sharing different parts of their environment.