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<overview>

<p>A function should never be duplicated verbatim in several places in the code. Of course

the severity of this anti-pattern is higher for longer functions than for extremely short

functions of one or two statements, but there are usually better ways of achieving the same

effect.</p>

</overview>

<recommendation>

<p>Code duplication in general is highly undesirable for a range of reasons: The artificially

inflated amount of code hinders comprehension, and ranges of similar but subtly different lines

can mask the real purpose or intention behind a function. There's also an omnipresent risk of

update anomalies, where only one of several copies of the code is updated to address a defect or

add a feature.</p>

<p>In the case of function duplication, how to address the issue depends on the functions themselves

and on the precise classes or modules in which the duplication occurs. At its simplest, the duplication can

be addressed by simply removing all but one of the duplicate function definitions and making

callers of the removed functions refer to the (now canonical) single remaining definition

instead.</p>

<p>This may not be possible for reasons of accessibility. A common example might

be where two classes implement the same functionality but neither is a subtype of the other,

so it is not possible to inherit a single method definition. In such cases, introducing a

common superclass to share the duplicated code is a viable option. Alternatively, if the methods

don't need access to private object state, they can be moved to a module-level function.</p>

</recommendation>

<references>

<li>Elmar Juergens, Florian Deissenboeck, Benjamin Hummel, and Stefan Wagner. 2009.

Do code clones matter? In <em>Proceedings of the 31st International Conference on

Software Engineering</em> (ICSE '09). IEEE Computer Society, Washington, DC, USA,

485-495.</li>

</references>

</qhelp>