Design patterns and SOLID principles

Design patterns and SOLID principles are ways to reason about code structure. They can reduce repetition and make changes easier, but neither one guarantees good design. A pattern that does not fit the problem adds indirection.

Design patterns

Design patterns describe common approaches to recurring design problems. They give a team shared names and starting points, not finished code. Their value depends on the problem and the language, so applying one just because it is familiar can make a small feature harder to follow.

Used well, patterns can make problem-solving more deliberate, allow code to be reused, and make maintenance easier. They are not a substitute for understanding the code around them.

SOLID principles

SOLID is an acronym for five principles used in object-oriented programming and design:

1. Single Responsibility: A class or module should have one reason to change.
2. Open-Closed: Code should be open for extension without requiring changes to stable behavior in every new case.
3. Liskov Substitution: A subtype should be usable wherever its base type is expected without weakening the expected behavior.
4. Interface Segregation: Clients should not depend on methods they do not use, so smaller interfaces are often easier to work with.
5. Dependency Inversion: High-level policy should depend on abstractions rather than on specific low-level implementations.

These principles can support modular and understandable code, but they are guidelines rather than a checklist. A small program does not need an abstraction for every concept, and applying all five at once can make code harder to read.

Use them deliberately

Start by studying common patterns in the language or framework you use. Apply a pattern when the problem calls for it, not because a catalog says it exists. Then revise the design when feedback or new requirements expose a real problem.

Continuous improvement in software comes from reading, changing, and reviewing code over time. More patterns do not automatically make a system easier to maintain.