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type-design-performance

Apply .NET type design rules to reduce allocations and improve runtime performance.

Updated Mar 3, 2026
Search Tags:#performance#dotnet#sealed-classes#static-pure-functions#type-design#readonly-structs#defer-enumeration
One-click install
npx skills add https://github.com/Thorstensen/claude-template --skill type-design-performance-thorstensen
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: type-design-performance
Source: https://github.com/Thorstensen/claude-template/tree/main/.claude/skills/csharp-type-design-performance
Command: npx skills add https://github.com/Thorstensen/claude-template --skill type-design-performance-thorstensen

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

Helps teams reduce performance pitfalls caused by non-sealed types, mutable state, and improper collection choices.

Core Features & Use Cases

  • Sealing classes by default to enable JIT devirtualization and communicate API intent.
  • Prefer readonly structs for immutable value types to avoid defensive copies.
  • Favor static pure functions for better testability and predictable performance.
  • Defer enumeration and return immutable collections at API boundaries.
  • Use case: when designing a high-throughput API or reviewing performance hotspots in existing code.

Quick Start

Apply these guidelines when starting a new API design: seal non-inheritance types, use readonly structs for immutable value types, implement static pure functions, defer enumeration, and return immutable collections.

Frequently Asked Questions about type-design-performance

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I design high-performance .NET types to minimize allocations?▼

Design high-performance .NET types by sealing non-inheritance classes, adopting readonly structs, implementing static pure functions, and returning immutable collections to minimize runtime allocations.

Why should I seal classes by default in .NET API design?▼

Sealing classes by default enables JIT devirtualization and clearly communicates API intent, which improves runtime performance and prevents unintended inheritance in high-throughput .NET APIs.

When should I use readonly structs over regular structs in .NET?▼

Use readonly structs for immutable value types to avoid defensive copies and ensure predictable performance when designing high-performance .NET APIs.

What is the best way to handle enumeration at API boundaries in .NET?▼

Defer enumeration and return immutable collections at API boundaries to maximize performance and prevent unexpected mutations when designing high-throughput .NET APIs.

How do I choose between class, struct, and record for performance hotspots?▼

Choose between class, struct, and record by evaluating allocation requirements and mutability, preferring sealed classes and readonly structs to optimize performance hotspots in .NET.

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