Positive wording in Boolean names

[Ursego]

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by Ursego » 21 Feb 2013, 21:37

Give Boolean DB fields, variables and functions positive names. Avoid both - direct negation ("NOT something") and words which carry a tinge of negativity (like "unissued" instead of "issued").

Think positively! That will simplify reading and understanding of Boolean expressions, especially if they are nested.

For example, compare the expressions if !docNotPrinted() and if docPrinted(): they are logically equivalent, but the positive version is easier to understand. As you see, the difference appears even when the expressions are stand-alone, but imagine if they would be a part of a complex Boolean expression!

What if we want to ask if the document has not been printed? Is if !docPrinted() better than if docNotPrinted()? Ok, we always have a chance that our Boolean var or method will be used with NOT, but a positive wording will result in ONE negation in the worst case scenario, while a negative wording will result in TWO - "negation of negation", which can be confusing and bug-prone !

Negative words are not as problematic as the direct negation, but it's better to avoid them too. The following list contains a few typical examples of NEGATIVE WORDS (TO AVOID) and POSITIVE WORDS (TO USE INSTEAD):

closed -> open
hidden -> displayed (shown)
failed -> ok (succeeded, successful)
doesntExist (absent, missing, omitted) -> exists
expired -> inEffect

Do not use negative prefixes in names:

excluded -> included
disabled -> enabled
disallowed (prohibited) -> allowed
nonStandard -> standard
unchecked -> checked
undefined -> defined

Here we discuss only Boolean identifiers. Of course, it's absolutely ok to use negative words in the names of non-Boolean DB fields and variables (like expiredPoliciesNum) and even Boolean if the negative word if not a part of the flag but describes the flagged entity (like hiddenChargesExist or failedBatchJobRegistered). Also, this rule has nothing to do with non-Boolean functions which perform negative actions - their names should describe exactly what the functions do (like disableSaveButton, prohibitPrinting, excludeInactiveCustomers, expirePolicy).