Code Smells Catalog

Afraid To Fail

Tue, 19 Apr 2022 00:00:00 GMT

Every caller has to check whether things actually worked, because this code returns status codes instead of throwing exceptions. The defensive ifs cascade up the entire call chain.

Alternative Classes with Different Interfaces

Tue, 19 Apr 2022 00:00:00 GMT

Two classes. Same job. Different spelling. One says hug_zombie(), the other says hug_snowman(), and neither realizes they're duplicating logic behind method names that could share a single interface.

Base Class depends on Subclass

Tue, 19 Apr 2022 00:00:00 GMT

When a parent class reaches down to reference its own children, the inheritance tree grows upside down. Change a leaf, redeploy the trunk.

Binary Operator in Name

Tue, 19 Apr 2022 00:00:00 GMT

If a method has "and" or "or" in its name, it's confessing to doing two things, and that confession is an invitation to split it in half.

Boolean Blindness

Tue, 19 Apr 2022 00:00:00 GMT

Does filter(true) mean take or drop? When a function operates on raw booleans, it destroys the information about what those values represent. The type system knows; the reader doesn't.

Callback Hell

Tue, 19 Apr 2022 00:00:00 GMT

Nested callbacks indented so deep the closing brackets cascade like a staircase to nowhere. The actual logic hides somewhere around indent level five.

Clever Code

Tue, 19 Apr 2022 00:00:00 GMT

Code that works but makes you feel stupid for not understanding it. Reinvented built-ins, abused language quirks, logic compacted into one-liners that nobody else can maintain.

Combinatorial Explosion

Tue, 19 Apr 2022 00:00:00 GMT

Dozens of methods that do almost the same thing, each differing by one small detail. Add a new feature and the count multiplies again. Good luck remembering which variant handles which edge case.

Complicated Boolean Expression

Tue, 19 Apr 2022 00:00:00 GMT

Reading it feels like solving a discrete math problem. The if-statement just checks whether a timer expired, but between the negations and conjunctions, you'd never guess that at a glance.

Complicated Regex Expression

Tue, 19 Apr 2022 00:00:00 GMT

A regex pattern so dense it needs an online decomposer to parse. Named variables and a builder function would make the same expression self-documenting.

Conditional Complexity

Tue, 19 Apr 2022 00:00:00 GMT

The if/else chain that grows a new branch with every feature. First it's readable. Then it's manageable. Then it's a 200-line switch statement, and suddenly the polymorphism refactor everyone avoided is the only option left.

Data Clump

Tue, 19 Apr 2022 00:00:00 GMT

red, green, and blue passed separately to every function that needs a color. The same variables travel together everywhere, never packaged into the object they're quietly begging to become.

Dead Code

Tue, 19 Apr 2022 00:00:00 GMT

You read past it wondering if it's safe to delete. Unreachable branches, commented-out blocks, functions that last ran in 2019. They cost nothing at runtime but tax every developer who encounters them.

Divergent Change

Tue, 19 Apr 2022 00:00:00 GMT

A class that changes for database reasons on Monday, calculation reasons on Wednesday, and display reasons on Friday. Same file, different reasons, and the merge conflicts pile up every sprint.

Dubious Abstraction

Tue, 19 Apr 2022 00:00:00 GMT

A method that orchestrates a business workflow but also opens its own database connection, mixing strategy with plumbing until you can't tell what level of abstraction you're reading.

Duplicated Code

Tue, 19 Apr 2022 00:00:00 GMT

The same logic in five places. Change one, miss another, and watch the behavior quietly diverge. According to Fowler, this is the single worst smell in a codebase.

Fallacious Comment

Tue, 19 Apr 2022 00:00:00 GMT

A comment that was true once but now lies. The code changed, the comment didn't, and there's no linter that catches the drift.

Fallacious Method Name

Tue, 19 Apr 2022 00:00:00 GMT

getItems() returns a single item. isValid() returns a string. setValue() quietly returns a value too. Method names that betray every convention programmers have built over decades.

Fate over Action

Tue, 19 Apr 2022 00:00:00 GMT

A class that holds data but owns none of the behavior operating on it. External code reaches in, pulls values out, and makes decisions the object never learned to make for itself.

Feature Envy

Tue, 19 Apr 2022 00:00:00 GMT

A method that touches another class's fields more than its own. It was written in the wrong place and belongs closer to the data it can't stop reaching for.

Flag Argument

Tue, 19 Apr 2022 00:00:00 GMT

A boolean parameter that forces the caller to write book(marcel, false) — and everyone who reads it to wonder: false what?

Global Data

Tue, 19 Apr 2022 00:00:00 GMT

Any code, anywhere, can read and write these variables. When something breaks, every function in the codebase is a suspect.

Hidden Dependencies

Tue, 19 Apr 2022 00:00:00 GMT

The class works perfectly in the developer's environment and crashes in production. You read the stack trace, search every constructor, and find nothing. The dependency was silently resolved from the environment.

Imperative Loops

Tue, 19 Apr 2022 00:00:00 GMT

for(i=0; i

Inappropriate Static

Tue, 19 Apr 2022 00:00:00 GMT

Impossible to override. Painful to mock. Silently coupling everything that calls them. Static methods are convenient right up until the behavior needs to vary: then they're a dead end.

Incomplete Library Class

Tue, 19 Apr 2022 00:00:00 GMT

A third-party library that does 95% of what you need. The missing 5% means building workarounds that duplicate effort, drift from the original, and never feel like first-class code.

Inconsistent Names

Tue, 19 Apr 2022 00:00:00 GMT

The mental shortcuts that let developers navigate by pattern break when one class calls it store(), another says add(), and a third insists on put(). Same operation. Three names. Zero muscle memory.

Inconsistent Style

Tue, 19 Apr 2022 00:00:00 GMT

Mixed formatting, flipped parameter orders, and clashing conventions in the same codebase. The code works, but the inconsistency saps trust. If they couldn't agree on style, what else didn't they agree on?

Indecent Exposure

Tue, 19 Apr 2022 00:00:00 GMT

Everything's public. Nothing's hidden. Other modules couple to implementation details they were never meant to see, and now you can't change a private algorithm without breaking six callers who shouldn't have known it existed.

Insider Trading

Tue, 19 Apr 2022 00:00:00 GMT

Two classes exchanging private implementation details they shouldn't have access to — the kind of under-the-table knowledge sharing that makes either one impossible to change without breaking the other.

Large Class

Tue, 19 Apr 2022 00:00:00 GMT

The God Class. Too many methods, too many fields, too many reasons to exist. Reading it takes a morning, testing it takes a sprint, and changing it is a gamble that affects everything it touches.

Lazy Element

Tue, 19 Apr 2022 00:00:00 GMT

The meeting that could have been an email — except it's a class. One field, one method that just delegates to another, an abstraction that costs more in complexity than it ever returns in clarity.

Long Method

Tue, 19 Apr 2022 00:00:00 GMT

A method so long you scroll past the beginning before reaching the end. Every change requires re-reading the whole thing, every piece of logic is trapped inside, and the side effects could be hiding three screens away.

Long Parameter List

Tue, 19 Apr 2022 00:00:00 GMT

Five arguments. Six. Seven. At some point the function signature becomes a riddle, the caller needs a cheat sheet, and the method is clearly trying to do more than one thing.

Magic Number

Tue, 19 Apr 2022 00:00:00 GMT

A bare 86400 in the code — is that seconds in a day, a timeout, or a config limit? Unnamed numbers hide intent, and when the same literal appears in five places, changing one means hunting for the rest.

Message Chain

Tue, 19 Apr 2022 00:00:00 GMT

object.getA().getB().getC().getD() — the caller knows the entire relationship chain, and every intermediate link becomes a dependency that breaks when any relationship changes.

Middle Man

Tue, 19 Apr 2022 00:00:00 GMT

Half its methods just call the same method on another class. It exists, it delegates, and its author can't explain what it adds. Remove it, and nothing breaks.

Mutable Data

Tue, 19 Apr 2022 00:00:00 GMT

Data that anything can modify at any time. The bug reproduces instantly in production and vanishes in your debugger — by the time you pause execution, something else already changed the value.

Null Check

Tue, 19 Apr 2022 00:00:00 GMT

Defensive null checks scattered everywhere like a nervous tic — each one a band-aid over a missing Null Object, and each a reminder that Tony Hoare called his invention a billion-dollar mistake.

Obscured Intent

Tue, 19 Apr 2022 00:00:00 GMT

You stare at the function for five minutes before realizing it calculates overtime pay. Between the single-letter variables, the magic numbers, and the missing whitespace, the intent is buried under layers of accidental obfuscation.

Oddball Solution

Tue, 19 Apr 2022 00:00:00 GMT

Same problem, two solutions, different files. One uses an adapter, the other rolls its own socket logic, and you can't tell which approach is the correct one. Or if either is.

Parallel Inheritance Hierarchies

Tue, 19 Apr 2022 00:00:00 GMT

Add a BasicUser, and you need a BasicFunctions. Add a PremiumUser, and here comes PremiumFunctions. Every subclass in one hierarchy demands a mirror in the other, and the cost of every new feature doubles.

Primitive Obsession

Tue, 19 Apr 2022 00:00:00 GMT

A phone number stored as a string. A price stored as a float. Concepts that deserve their own types get crammed into primitives, losing validation, scattering logic, and pretending a bare string is something it's not.

Refused Bequest

Tue, 19 Apr 2022 00:00:00 GMT

A Tower that extends Minion but throws NotImplemented on move(). The inheritance contract promises full support; the subclass delivers a runtime exception and an apology.

Required Setup or Teardown Code

Tue, 19 Apr 2022 00:00:00 GMT

Close the socket when you're done. Check the environment variables before you start. Reset the state after every call. The object could handle all of this internally. Instead, it made it your problem.

Shotgun Surgery

Tue, 19 Apr 2022 00:00:00 GMT

One small feature change. A dozen files to edit. You submit the PR, then find two more files you missed.

Side Effects

Tue, 19 Apr 2022 00:00:00 GMT

set_gold(amount) sounds simple enough. Except it also triggers a dancing animation and resets the payday timer. Methods that do more than their name promises hide behavior callers never asked for and debuggers never suspect.

Special Case

Tue, 19 Apr 2022 00:00:00 GMT

The if-statement that handles "one weird edge case" before the real logic begins. It was a hotfix once. It was never properly refactored. Now every future reader has to hold that branch in their head alongside everything else.

Speculative Generality

Tue, 19 Apr 2022 00:00:00 GMT

An abstract base class for a hierarchy that never grew. Three extra parameters for a feature you were sure someone would request. Abstractions built for a future that never arrived, cluttering the code with unused generality.

Status Variable

Tue, 19 Apr 2022 00:00:00 GMT

found = False. Then a loop. Then found = True somewhere inside. Then a check after. Mutable flags that complicate control flow when a direct return or a built-in would express the same logic in a single line.

Temporary Field

Tue, 19 Apr 2022 00:00:00 GMT

A field that's null eleven months of the year and suddenly matters during one specific calculation. The object carries it everywhere, for one brief moment of relevance.

Tramp Data

Tue, 19 Apr 2022 00:00:00 GMT

Data hitchhiking through a chain of methods that never use it. Each function accepts the parameter, ignores it, and passes it along — just so the one at the end of the line can finally read it.

Type Embedded in Name

Tue, 19 Apr 2022 00:00:00 GMT

playerName, dateString, userList: the type is already in the annotation, and now it's in the name too. Redundant today, misleading tomorrow when the type changes but the name doesn't.

Uncommunicative Name

Tue, 19 Apr 2022 00:00:00 GMT

data, val, m1, temp, get_f(). The code compiles fine. Understanding it requires reverse-engineering every abbreviation the original author thought was self-evident.

Vertical Separation

Tue, 19 Apr 2022 00:00:00 GMT

Variables declared at the top of a method, used fifty lines later. By the time you reach the logic that needs them, you've already forgotten what half the variables were for.

"What" Comment

Tue, 19 Apr 2022 00:00:00 GMT

Comments that narrate what the code does instead of why — a deodorant sprayed over smelly code, where extracting a well-named method would eliminate both the smell and the comment.