Data Clump

Data Clumps refer to a situation in which a few variables are passed around many times in the codebase instead of being packed into a separate object. Think of it as having to hold different groceries in a grocery store by hand instead of putting them into a basket or at least a handy cardboard box - this is just not convenient. Any set of data items that are permanently or almost always used together, but are not organized jointly, should be packed into a class. An example could be the RGB values held separately rather than in an RGB object.

Causation

Developers often believe that a pair of variables is unworthy of creating a separate instance for them that could aggregate them under a common abstraction [1].

Problems

Hidden Abstraction

Variables grouped into objects of their own increase the readability of the code, thus making the concept clearer.

More Complex APIs

Components Interfaces complexity increases with the number of accepted data

Example

def colorize(red: int, green: int, blue: int):
    ...

@dataclass(frozen=True)
class RGB:
    red: int
    green: int
    blue: int


def colorize(rgb: RGB):
    ...

Refactoring:

• Extract Class (and additionally, maybe there is the possibility for Move Method)
• Introduce Parameter Object

Sources

• [1] - William C. Wake, "Refactoring Workbook" (2004)
• [Origin] - Martin Fowler, "Refactoring: Improving the Design of Existing Code" (1999)