Data Clumps

Groups of data that appear together repeatedly.

“Bunches of data that hang around together really ought to be made into their own object.” – Fowler & Beck

(x, y), (street, city, zip), (startDate, endDate).

Signs of Use (Symptoms)

  • Same 3-4 variables passed together to multiple functions.
  • Same 3-4 fields appearing in multiple classes.

Why it is bad (Consequences)

  • Duplication: Same grouping logic repeated.
  • Missed Abstraction: The concept (e.g., DateRange, Address) is not explicitly named.

Why it happens (Root Cause)

Easier to pass loose variables than to create a class.

When it might be okay (Exceptions)

  • Rarely. If it happens once, maybe. If it happens twice, extract it.

Explanation

Problem

You pass startDate and endDate to 10 functions. They always travel together.

The Flaw

You’re not giving a name to the concept. DateRange is a thing. Acknowledge it.

Real world analogy

A key and a keychain. If you always carry them together, attach them!

Refactoring Solution

  • Extract Class: Create a Value Object (e.g., DateRange, Coordinates, Address).
  • Introduce Parameter Object.

Pros and Cons (of the Antipattern)

Pros (Why people do it) Cons (The price you pay)
  • Less upfront work
    		•
  • Duplication
  • Inconsistency
    		•

    Comparison

    • Related Antipatterns: Primitive Obsession, Long Parameter List.
    • Related Principles: DRY.

    Code example

    Typescript

    Bad (The Antipattern)

    Good (The Fix)

    PHP

    Bad (The Antipattern)

    Good (The Fix)