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### 9.6 Functions

A function is represented by a `FUNCTION_DECL` node. A set of overloaded functions is sometimes represented by a `OVERLOAD` node.

An `OVERLOAD` node is not a declaration, so none of the DECL_ macros should be used on an `OVERLOAD`. An `OVERLOAD` node is similar to a `TREE_LIST`. Use `OVL_CURRENT` to get the function associated with an `OVERLOAD` node; use `OVL_NEXT` to get the next `OVERLOAD` node in the list of overloaded functions. The macros `OVL_CURRENT` and `OVL_NEXT` are actually polymorphic; you can use them to work with `FUNCTION_DECL` nodes as well as with overloads. In the case of a `FUNCTION_DECL`, `OVL_CURRENT` will always return the function itself, and `OVL_NEXT` will always be `NULL_TREE`.

To determine the scope of a function, you can use the `DECL_CONTEXT` macro. This macro will return the class (either a `RECORD_TYPE` or a `UNION_TYPE`) or namespace (a `NAMESPACE_DECL`) of which the function is a member. For a virtual function, this macro returns the class in which the function was actually defined, not the base class in which the virtual declaration occurred.

If a friend function is defined in a class scope, the `DECL_FRIEND_CONTEXT` macro can be used to determine the class in which it was defined. For example, in

         class C { friend void f() {} };

the `DECL_CONTEXT` for `f` will be the `global_namespace`, but the `DECL_FRIEND_CONTEXT` will be the `RECORD_TYPE` for `C`.

In C, the `DECL_CONTEXT` for a function maybe another function. This representation indicates that the GNU nested function extension is in use. For details on the semantics of nested functions, see the GCC Manual. The nested function can refer to local variables in its containing function. Such references are not explicitly marked in the tree structure; back ends must look at the `DECL_CONTEXT` for the referenced `VAR_DECL`. If the `DECL_CONTEXT` for the referenced `VAR_DECL` is not the same as the function currently being processed, and neither `DECL_EXTERNAL` nor `DECL_STATIC` hold, then the reference is to a local variable in a containing function, and the back end must take appropriate action.