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csharp-best-practices

Modern .NET and C# best practices for code quality, performance, and correctness. USE FOR: choosing struct/class/record/readonly-record-struct; nullable reference types; pattern matching; primary constructors; collection expressions; required members; init-only properties; file-scoped namespaces; global usings; async/await patterns; ConfigureAwait; ValueTask vs Task; CancellationToken propagation; IAsyncEnumerable; Span<T>/Memory<T> usage; avoiding boxing; readonly struct; ArrayPool<T>; FrozenDictionary/FrozenSet; LINQ vs loops in hot paths; ArgumentNullException.ThrowIfNull; ThrowIfNegative; ThrowIfZero; IReadOnlyList return types; error handling patterns; GeneratedRegex; LoggerMessage; source generators for regex and logging; avoiding Math/MathF in favor of static methods on the numeric type. DO NOT USE FOR: generic math interfaces (use dotnet-generic-math); ASP.NET Core middleware; EF Core modeling.

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NetFabric/NetFabric.Numerics36 stars(GitHub 36 + cccskills 0)

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See how to install

Files included (5)

SKILL.md4.7 KB
references/async.md3.8 KB
references/language-features.md3.9 KB
references/performance.md4.2 KB
references/source-generators.md3.5 KB

SKILL.md (original)

Review the instructions the agent will receive before you install.

C# Best Practices

Targets .NET 8+ / C# 12+ unless noted.

Type Selection

Scenario	Preferred type
Small immutable value (<4 fields)	`readonly record struct`
Value type, mutated in place	`struct` (avoid) or `ref struct`
Mutable reference type	`class`
Immutable data transfer	`record class`
Stack-only lifetime	`ref struct`

Language Features Quick-Ref

Feature	Version	Note
`required` members	C# 11	enforce init in object initializer
Primary constructors	C# 12	classes & structs; params are in-scope everywhere
Collection expressions `[1, 2, 3]`	C# 12	replaces `new List<>`, `new[]`, `Array.Empty<>`
Raw string literals `"""..."""`	C# 11	no escape sequences needed
Pattern matching (`switch` expr)	C# 8+	prefer over `if/else` chains on type/value
`is` type patterns	C# 9	`if (x is Foo { Bar: > 0 } f)`
`nameof()`	C# 6	always use for param names in exceptions
File-scoped namespace	C# 10	`namespace Foo;` — one per file
Global usings	C# 10	put in `GlobalUsings.cs`
`init`-only setters	C# 9	immutable after construction

Full examples → references/language-features.md

Nullability

Enable project-wide: <Nullable>enable</Nullable> in .csproj
Use ! only when null is provably impossible; prefer null checks
ArgumentNullException.ThrowIfNull(param) — validates & throws in one line
Return T? from "not found" lookups; never return null for empty collections (return empty)

Error Handling

Validator	.NET version
`ArgumentNullException.ThrowIfNull(x)`	.NET 6
`ArgumentOutOfRangeException.ThrowIfNegative(x)`	.NET 8
`ArgumentOutOfRangeException.ThrowIfZero(x)`	.NET 8
`ArgumentOutOfRangeException.ThrowIfGreaterThan(x, max)`	.NET 8
`ObjectDisposedException.ThrowIf(condition, this)`	.NET 7

Source Generators

Pattern	Attribute	Benefit
Regex	`[GeneratedRegex("...")]` on `static partial` method	Compile-time; no runtime compilation; faster
Logging	`[LoggerMessage(...)]` on `static partial` method	Zero-alloc structured logging; no boxing

Full examples → references/source-generators.md

API Design

Return IReadOnlyList<T> / IReadOnlyDictionary<K,V> for collections
Accept IEnumerable<T> for input (widest contract)
Accept ReadOnlySpan<T> overloads for hot paths
Use CancellationToken as last parameter; default to default

Math APIs

Never call Math.* or MathF.* — use the equivalent static method on the operand's own type instead (double.Sqrt(x), float.Pow(x, y), int.Abs(x)), available since .NET 7 via INumber<T>/IFloatingPointIeee754<T>
Same rule applies generically: T.Sqrt(x) when T : IRootFunctions<T> — avoids picking the wrong precision and works uniformly across float/double/custom numeric types
Full generic-math interface usage (INumber<T>, IFloatingPointIeee754<T>, etc.) → use the dotnet-generic-math skill

Reference Files

File	Load When
references/language-features.md	Records, pattern matching, primary constructors, collection expressions, raw strings
references/performance.md	Span, Memory, ArrayPool, stackalloc, boxing, FrozenDictionary, LINQ vs loops
references/async.md	async/await, ValueTask, ConfigureAwait, IAsyncEnumerable, CancellationToken
references/source-generators.md	GeneratedRegex, LoggerMessage

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Install

Install with a command

npx skills add https://github.com/NetFabric/NetFabric.Numerics --skill csharp-best-practices

Paste it into your terminal and run it (requires Node.js). You can choose which agents to install it for, such as Claude Code or Codex.

Ask your agent

Please install the following Agent Skill.
https://github.com/NetFabric/NetFabric.Numerics/tree/main/.agents/skills/csharp-best-practices

First review SKILL.md and the bundled files and confirm there is nothing suspicious (such as sending data externally or reading credentials). Then place it in ~/.claude/skills/csharp-best-practices/ for Claude Code, or ~/.agents/skills/csharp-best-practices/ for Codex.

Send this text to Claude Code or Codex as is. It checks the contents before installing.

View source on GitHub

Repository: NetFabric/NetFabric.Numerics
Stars: 36
Forks: 1
Category: Productivity
License: MIT
Original language: English
Last updated: Aug 10, 2026

A skill is a set of instructions and scripts for an agent. cccskills does not guarantee that skills are safe. Review the contents before you install.