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Performance

Built-in Types

DateTime

  • Do NOT use DateTime.Now() as it determines the current time and then translates it to the system timezone. Instead use DateTime.UtcNow. Better yet, create a simple wrapper class so its possible to inject it and configure it with a timezone.

Nulls

  • Do not use Null Coalescing fallbacks which allocate memory, instead use Enumerable.Empty() and Array.Empty().
Method Description Allocates New Memory?
Enumerable.Empty<T>() Returns a cached, reusable empty IEnumerable<T> ❌ No
Array.Empty<T>() Returns a cached, reusable empty T[] ❌ No
new T[0] Creates a new empty array each time ✅ Yes
new List<T> Creates a new empty List each time ✅ Yes

Examples:

string[]? names = GetNamesOrNull();

// Safer fallback
foreach (var name in names ?? Array.Empty<string>())
{
    Console.WriteLine(name);
}

public void ProcessData(IEnumerable<int>? data = null)
{
    foreach (var number in data ?? Enumerable.Empty<int>())
    {
        Console.WriteLine(number);
    }
}

When to Use Which?

  • ✅ Enumerable.Empty<T>(): when your logic depends on IEnumerable<T> (e.g., LINQ).
  • ✅ Array.Empty<T>(): when you need a real array (e.g., indexing, passing to APIs expecting T[]).

String

  • Use String.Conact() instead of manually appending to the string with "+"

Using String.Concat("this", "is", "a", "string") is generally more efficient than using the + operator repeatedly, especially in loops or when concatenating many strings.

That's because + creates intermediate string objects for each operation, while String.Concat directly combines them in one go, reducing memory allocations and improving performance.