IfSQ

SPM-1—Magic Numbers

Defect Indicators: Numeric literals (other than 0 or 1) have been embedded directly into the source code. For example “34” or “86400”.

Risks: If numbers are embedded in code in this way, it increases the time needed to make maintenance changes, and increases the risk of error.

Assessment:

• Mark all the lines that contain an unexplained numeric literal other than 0 (zero) or 1 (one).

Remedy: Isolate a single copy of the number and refer to it. For example, isolate the number into:

• a local constant or enumerated type
• a global constant or enumerated type
• a constant class
• an initialisation file

Note: If your programming language does not support constants, simulate this—for example, by declaring a variable and initialising it at the beginning of the program.

References:

• The Pragmatic Programmer (Andrew Hunt, and David Thomas), 2000.

Research Findings:

• Don't Repeat Yourself (DRY):
  The DRY principle: Don't Repeat Yourself.