Patterns with a cost

Composition, small interfaces and functions often implement strategy, adapter and decorator without an inheritance hierarchy. A function can express a policy; an io.Reader wrapper can add counting or limits around another reader.

Functional options can manage optional constructor settings, but required dependencies should remain obvious. A singleton that silently owns a database client hides lifetime and makes parallel tests harder; explicit construction is often clearer.

Use a pattern to solve an identified pressure. Explain the extra indirection, configuration ordering and error behavior. Prefer a direct implementation until two variations or a meaningful boundary justify abstraction.