Use indexer instead of LINQ method

This is part of a series where I analyze .NET code quality rules from a performance perspective. Today, let’s talk about CA1826: Use property instead of Linq Enumerable method.

Rule description

This rule simply asks not to use First(), Last(), Count() methods from LINQ with IReadOnlyList<T>:

IReadOnlyList<string> list = ["str1", "str2", "str3"];
var first = list.First();   // CA1826
var last = list.Last();     // CA1826
var count = list.Count();   // CA1826

Instead, you should use indexer or Count property for better performance:

IReadOnlyList<string> list = ["str1", "str2", "str3"];
var first = list[0];
var last = list[^1];
var count = list.Count;

Performance analysis

I wrote a simple benchmark to see how much LINQ methods really affect performance. The results are in the repo and on the diagram below.

As you can see, there’s a difference between LINQ and direct access. But the difference is very small — just a few microseconds on my machine.

Should you care?

In most cases, no. The performance gain is small. But if you’re writing high-performance code, or these LINQ methods appear in a loop, it might be worth to refactor your code.