csharp-type-design-performance

Design high-performance .NET types by sealing classes by default to enable JIT devirtualization and inlining. Use readonly structs for small immutable value types and prefer static pure functions to reduce state overhead.

Use readonly structs for small immutable value types in C# to prevent defensive copying and ensure memory layout efficiency. This pattern minimizes allocations and defends against accidental mutation when passing data across API boundaries.

The best way to return immutable collections at .NET API boundaries is to defer enumeration and output immutable types. This prevents callers from mutating internal state, reduces memory allocations, and ensures safe, fast API responses.

Sealing classes by default improves C# API performance and clarity by enabling JIT inlining and preventing uncontrolled inheritance. This restricts extensibility to explicitly designed points, ensuring robust library development.

Review .NET types for performance improvements and deferred enumeration when developing performance-critical components, APIs, or libraries where memory layout and allocation overhead matter. Switching to static pure functions and deferred enumeration optimizes execution.

Static pure functions limit state management, requiring all necessary data to be passed as parameters rather than stored internally. This improves testability and reduces side effects but may complicate APIs heavily reliant on shared state.