Give practical .NET examples of Strategy, Adapter, and Decorator, and explain how you would choose between them.

Choose Strategy, Adapter, and Decorator for real problems

Selects small structural and behavioral patterns from the problem being solved instead of pattern-name recognition.

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TL;DR

I might use Strategy for choosing a shipping-price policy, Adapter for presenting a vendor payment SDK as the application's payment port, and Decorator for adding telemetry or caching around an existing implementation. I choose from the design pressure: variable behavior, incompatible interfaces, or cross-cutting behavior around one operation. The class shape can look similar, so intent and contract matter more than the name.

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Strategy, Adapter, Decorator, intent, composition, DI registration, and avoiding pattern-driven design.

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Core answer
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Why this question matters
The patterns solve different problems. Strategy varies an algorithm, Adapter translates one contract into another, and Decorator wraps the same contract to add behavior.
I might use Strategy for choosing a shipping-price policy, Adapter for presenting a vendor payment SDK as the application's payment port, and Decorator for adding telemetry or caching around an existing implementation. I choose from the design pressure: variable behavior, incompatible interfaces, or cross-cutting behavior around one operation. The class shape can look similar, so intent and contract matter more than the name.
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Stronger answer
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A strategy selector should have bounded, validated choices. An adapter owns translation, including errors and provider-specific semantics, rather than leaking them to callers. A decorator preserves the wrapped contract and should be explicit about order when several are composed, such as authorization before caching or telemetry around retries. Dependency injection can assemble these patterns, but registration should remain readable and deterministic.

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Use these to catch weak phrasing, shallow reasoning, and risky claims.

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Details

Choosing a pattern by class diagram similarity.
Letting adapters leak vendor models.
Composing decorators in accidental registration order.
Using Strategy for unbounded configuration rules.

Give practical .NET examples of Strategy, Adapter, and Decorator, and explain how you would choose between them.

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