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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.

日本語の概要は準備中です。原文の説明を表示しています。

NetFabric/NetFabric.Numericsスター 36(GitHub 36 + cccskills 0)

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含まれるファイル（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（原文）

インストールする前に、エージェントに与えられる指示の中身を確認できます。

C# Best Practices

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

Type Selection

ScenarioPreferred type
Small immutable value (<4 fields)readonly record struct
Value type, mutated in placestruct (avoid) or ref struct
Mutable reference typeclass
Immutable data transferrecord class
Stack-only lifetimeref struct

Language Features Quick-Ref

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

PatternAttributeBenefit
Regex[GeneratedRegex("...")] on static partial methodCompile-time; no runtime compilation; faster
Logging[LoggerMessage(...)] on static partial methodZero-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

FileLoad When
references/language-features.mdRecords, pattern matching, primary constructors, collection expressions, raw strings
references/performance.mdSpan, Memory, ArrayPool, stackalloc, boxing, FrozenDictionary, LINQ vs loops
references/async.mdasync/await, ValueTask, ConfigureAwait, IAsyncEnumerable, CancellationToken
references/source-generators.mdGeneratedRegex, LoggerMessage

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日本語の概要は準備中です。原文の説明を表示しています。

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NetFabric/NetFabric.Numerics362026年8月10日 更新

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