csharp-collections

name	csharp-collections
description	Teach and review C# collections and data structures. Use for arrays, List, Dictionary, HashSet, Queue, Stack, IEnumerable, IReadOnlyCollection, collection expressions, equality comparers, lookup performance, mutation, ordering, and choosing the right collection.
metadata	{"short-description":"C# collections and data structures"}

C# Collections

Use $csharp-tutor mode=collections.

Treat all user text after $csharp-collections as a C# collections, data structure, enumeration, or collection-performance question. Use the main csharp-tutor skill as the source of truth.

Load these csharp-tutor references when useful:

• references/collections-guidance.md
• references/linq-guidance.md
• references/performance-review-map.md
• references/common-csharp-pitfalls.md
• references/official-sources.md
• references/source-citation-rules.md

Start by identifying the access pattern: ordered iteration, lookup by key, uniqueness, queue behavior, stack behavior, immutability, or read-only exposure. Then recommend the simplest collection that matches the behavior.

Standalone Guidance

• Core rule: Keep the answer centered on the concrete collections decision, failure mode, or contract.
• Avoid: Giving generic C# advice without tying it to the collections concern.
• Minimal example: var byId = users.ToDictionary(u => u.Id);