Loop-switch sequence

Quality 0.50 · 0 views · Updated 2 months ago

title: "Loop-switch sequence" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["computer-programming"] topic_path: "general/computer-programming" source: "https://en.wikipedia.org/wiki/Loop-switch_sequence" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

A loop-switch sequence (also known as the for-case paradigm or Anti-Duff's Device) is a programming antipattern where a clear set of steps is implemented as a switch-within-a-loop. The loop-switch sequence is a specific derivative of spaghetti code.

It is not necessarily an antipattern to use a switch statement within a loop—it is only considered incorrect when used to model a known sequence of steps. The most common example of the correct use of a switch within a loop is an inversion of control such as an event handler. In event handler loops, the sequence of events is not known at compile-time, so the repeated switch is both necessary and correct (see event-driven programming, event loop and event-driven finite state machine).

This is not a performance antipattern, though it may lead to an inconsequential performance penalty due to the lack of an unrolled loop. Rather, it is a clarity antipattern, as in any non-trivial example it is much more difficult to decipher the intent and actual function of the code than the more straightforward refactored solution.

Example

An event-driven solution would implement a listener interface: ::code[lang=java] String key = null; String value = null; List params = null; int column = 0;

public void addToken(token) {

// parse a key, a value, then three parameters 
switch (column) {
    case 0:
        params = new LinkedList<String>();
        key = token;
        break;
    case 1:
        value = token;
        break;
    default:
        params.add(token);
        break;
}
if (++column >= 5) {
    column = 0;
    completeRow(key, value, params);
}

} ::

But without the listener, it becomes an example of the antipattern: ::code[lang=java] // parse a key, a value, then three parameters String key = null; String value = null; List params = new LinkedList();

for (int i = 0; i < 5; i++) { switch (i) { case 0: key = stream.parse(); break; case 1: value = stream.parse(); break; default: params.add(stream.parse()); break; } } ::

And here is the refactored solution: ::code[lang=java] // parse a key and value String key = stream.parse(); String value = stream.parse();

// parse 3 parameters List params = new LinkedList(); for (int i = 0; i < 3; i++) { params.add(stream.parse()); } ::

References

References

  1. (30 November 2013). "Loop-switch sequences". LEVEL UP CODE.
  2. [http://thedailywtf.com/Articles/The_FOR-CASE_paradigm.aspx The FOR-CASE paradigm] and [http://thedailywtf.com/Articles/Switched_on_Loops.aspx Switched on Loops] at [[The Daily WTF]]

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::

computer-programming