Editing Reflective programming (section)

==Implementation==
{{Unreferenced section|date=January 2008}}
A language that supports reflection provides a number of features available at runtime that would otherwise be difficult to accomplish in a lower-level language. Some of these features are the abilities to:
* Discover and modify [[Source code|source-code]] constructions (such as code blocks, [[Class (computer science)|classes]], methods, protocols, etc.) as [[first-class object]]s at [[Runtime (program lifecycle phase)|runtime]].
* Convert a [[string (computer science)|string]] matching the symbolic name of a class or function into a reference to or invocation of that class or function.
* Evaluate a string as if it were a source-code statement at runtime.
* Create a new [[Interpreter (computing)|interpreter]] for the language's [[bytecode]] to give a new meaning or purpose for a programming construct.

These features can be implemented in different ways. In [[MOO (programming language)|MOO]], reflection forms a natural part of everyday programming idiom. When verbs (methods) are called, various variables such as ''verb'' (the name of the verb being called) and ''this'' (the object on which the verb is called) are populated to give the context of the call. Security is typically managed by accessing the caller stack programmatically: Since ''callers''() is a list of the methods by which the current verb was eventually called, performing tests on ''callers''()[0] (the command invoked by the original user) allows the verb to protect itself against unauthorised use.

Compiled languages rely on their runtime system to provide information about the source code. A compiled [[Objective-C]] executable, for example, records the names of all methods in a block of the executable, providing a table to correspond these with the underlying methods (or selectors for these methods) compiled into the program. In a compiled language that supports runtime creation of functions, such as [[Common Lisp]], the runtime environment must include a compiler or an interpreter.

Reflection can be implemented for languages without built-in reflection by using a [[program transformation]] system to define automated source-code changes.