Boolean Naming Conventions - samuelkripto/styleguide GitHub Wiki

Tags: #coding-standards #clean-code #best-practices

Summary: This guide establishes the standard for writing clear, readable boolean variables across our codebase.

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1. The Golden Rule

A boolean variable name should sound like a Yes/No question.

When placed inside a conditional statement (if), the code should read like a natural English sentence.

• ✅ Good: if (isOpen) -> Reads as: "If it is open..."
• ❌ Bad: if (open) -> Reads as: "If open..." (Ambiguous: Is this a command? A state?)

2. Choosing the Right Prefix

While is is the most common prefix, it is not always the most accurate. Choose the auxiliary verb that best describes the nature of the boolean.

A. State & Identity (is, has, uses, exists)

Use these for current properties or ownership.

Prefix	Usage	Example
is	General state or identity.	isValid, isVisible, isAdmin
has	Ownership or containment.	hasChildren, hasErrors, hasAccess
uses	Is it currently employing X?	usesEncryption, usesCache

Suffix	Usage	Example
exists	Existence checks (often DB/File).	fileExists, recordExists

B. Capabilities & Permissions (can, allows, supports, requires)

Use these to define what the system or user is able to do.

Prefix	Usage	Example
can	Ability to perform an action.	canExecute, canEdit
allows	Permission or policy settings.	allowsGuestAccess, allowsDuplicates
supports	Technical/Hardware features.	supportsBluetooth, supportsIPv6
requires	A hard dependency.	requiresAuth, requiresRestart

C. Lifecycle & Time (should, will, did, was, needs)

Use these for future intent, past history, or recommendations.

Prefix	Usage	Example
should	Recommendation/necessity (often UI).	shouldRender, shouldRetry
will	Definitive future outcome.	willOverwrite, willBlock
did	Completed action (history).	didFinish, didTimeout
was	Previous historical state.	wasCreated, wasSeen
needs	Requirement for a future state.	needsRefresh, needsMigration

D. Content (contains, includes, matches)

Use these for collections or string validation.

Prefix	Usage	Example
contains	Membership in a collection.	containsItem, containsSpecialChar
includes	Membership in a collection.	includesTax
matches	Regex or pattern conformance.	matchesFilter, matchesRegex

E. Plurals & Relationships (are)

Use this when checking the state of a group or a mutual relationship between multiple items.

Prefix	Usage	Example
are	Plural states or mutual links.	areFriends, areEqual, areAllReady

3. Anti-Patterns (What to Avoid)

🚫 The "Flag" Suffix

Do not put the type in the name. We know it's a boolean; tell us what it means.

• Bad: loginFlag, validStatus, checkBit
• Good: isLoggedIn, isValid, isChecked

🚫 Negatives

Keep logic positive. Standard convention is usually isEnabled.

• Bad: isDisabled, disallowsGuest, excludesItem
• Good: isEnabled, allowsGuest, includesItem

🚫 Double Negatives

Logic becomes incredibly hard to parse when you negate a negative variable.

• Bad: isNotEnabled (Checking !isNotEnabled is painful).
• Good: isEnabled

🚫 Ambiguous Nouns

A noun by itself usually implies an object (String, Class, Dictionary), not a boolean.

• Bad: user, answer, file
• Good: isUser, hasAnswer, fileExists

🚫 Third-person Singular Question Form

• Acceptable: doesFileExist (Valid, answers Yes/No), doesSupportHdr
• Better: fileExists, hasFile, supportsHdr

🚫 Commands

The word do is almost always a command.

• Bad: doLog, doUpdate (looks like a function name: function doUpdate() { ... })
• Good: shouldLog, isLoggingEnabled, isUpdated

4. Language-Specific Reference Table

Conventions vary slightly by language ecosystem. Adhere to the standard of the language you are writing in.

Language	Case Style	Convention Notes	Examples
JavaScript / TS	camelCase	Prefixes (is, has) strongly encouraged to distinguish from objects.	isLoading, shouldRender
Java / C#	camelCase	Strictly uses prefixes. For JavaBeans, getters must use is.	isValid, canExecute
Python	snake_case	PEP 8 standard. Prefixes are standard.	is_valid, has_permission
Ruby	snake_case	Exception: Methods ending in ? return booleans. Variables use is_.	valid? (method), is_admin
Go	CamelCase	Prefixes common, but omitted if struct/package provides context.	IsReady, HasPrefix
Rust	snake_case	Predicate methods must use prefixes per API guidelines.	is_empty, starts_with
Swift / Kotlin	camelCase	Reads like a sentence. Kotlin properties interop with Java is getters.	isUserInteractionEnabled
C / C++	Mixed	STL uses snake_case. Application code varies, but prefixes are standard.	is_open, has_value

5. Quick Check Checklist

Before committing, ask yourself:

• Does it start with a verb (is, has, can, etc.)?
• Does if (variableName) sound like a coherent English sentence?
• Is it positive? (Avoid isNot... or disable...)
• Is it free of type noise (Flag, Bit, Bool)?