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32 lines
1.6 KiB
XML
32 lines
1.6 KiB
XML
<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>If two files share a lot of code then there is a lot of unnecessary code duplication.
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This makes it difficult to make changes in future and makes the code less easy to read.</p>
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</overview>
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<recommendation>
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<p>While completely duplicated files are rare, they are usually a sign of a simple oversight.
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Usually the required action is to remove all but one of them. A common exception to this rule may
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arise from generated code that simply occurs in several places in the source tree; the check can be
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adapted to exclude such results.</p>
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<p>It is far more common to see duplication of many lines between two files, leaving just a few that
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are actually different. Consider such situations carefully. Are the differences deliberate or a
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result of an inconsistent update to one of the clones? If the latter, then treating the files as
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completely duplicate and eliminating one (while preserving any corrections or new features that may
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have been introduced) is the best course. If two files serve genuinely different purposes but almost
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all of their lines are the same, that can be a sign that there is a missing level of abstraction.
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Look for ways to share the functionality, by creating a new module for the common parts and
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importing that module into the original module.</p>
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</recommendation>
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<references>
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<li>E. Juergens, F. Deissenboeck, B. Hummel and S. Wagner, <em>Do Code Clones Matter?</em>, 2009. (<a href="https://wwwbroy.in.tum.de/~juergens/publications/ICSE2009_RP_0110_juergens.pdf">available online</a>).</li>
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</references>
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</qhelp>
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