csharp

C#: Idiomatic Efficiency Reference

When to Use

• Use this skill when the task matches this description: Language-specific super-code guidelines for csharp.

Table of Contents

1. [LINQ & Collections](#linq)
2. [Null Handling](#nulls)
3. [Async/Await](#async)
4. [Records & Pattern Matching](#records)
5. [Error Handling](#errors)
6. [Resource Management](#resources)
7. [Anti-patterns specific to C#](#antipatterns)

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1. LINQ & Collections {#linq}

// ❌ Imperative accumulation
var result = new List<string>();
foreach (var item in items) {
    if (item.IsActive) result.Add(item.Name.ToUpper());
}

// ✅
var result = items
    .Where(i => i.IsActive)
    .Select(i => i.Name.ToUpper())
    .ToList();

// ❌ Manual grouping
var grouped = new Dictionary<string, List<Item>>();
foreach (var item in items) {
    if (!grouped.ContainsKey(item.Category))
        grouped[item.Category] = new List<Item>();
    grouped[item.Category].Add(item);
}

// ✅
var grouped = items.GroupBy(i => i.Category)
    .ToDictionary(g => g.Key, g => g.ToList());

// ❌ Checking Any() then First()
if (items.Any(i => i.IsValid)) {
    var first = items.First(i => i.IsValid);
}

// ✅
var first = items.FirstOrDefault(i => i.IsValid);
if (first is not null) { ... }

Prefer method syntax for chains of 2+ operations. Query syntax is fine for complex joins.

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