Apply Strategy pattern for multiple payment methods
Reported in GitLab European engineering loops. OOD pattern question focused on replacing condition-heavy logic.
Interview scenario
Context for GitLab candidates:
Support card, UPI, wallet, and net banking with clean extensible design.
Model answer
Try answering aloud first
Cover trade-offs, structure, and a concrete example before revealing the baseline response.
How to frame this at GitLab: Connect your answer to measurable impact, clarity of thought, and trade-offs the team cares about. Below is a strong baseline response you can adapt with your own project examples.
Define a common PaymentStrategy interface with methods like authorize and capture. Concrete strategies implement provider-specific behavior while checkout flow depends only on the interface.
This removes large if-else branches and allows adding new methods without modifying stable orchestration code. Pair Strategy with factory or dependency injection to select implementation at runtime.
Interviewers like hearing about testability gains: each strategy can be unit tested independently with mocked gateway clients.
Discussion
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