Mastering the `let` Keyword in LINQ

In C#, the let keyword in LINQ queries is a neat way to store intermediate results inside a query. It keeps your code clean, readable, and avoids repeated calculations.

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How let Works

let allows you to define a temporary variable in your query that you can reuse later:

string[] words = { "one", "two", "three", "four", "five" };

var query =
    from w in words
    let length = w.Length
    where length > 3
    select new { Word = w, Length = length };

foreach (var item in query)
    Console.WriteLine($"{item.Word} - {item.Length}");

Output:

three - 5
four - 4
five - 4

Notice how let avoids repeating w.Length and makes the query cleaner.

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Practical Example: Finding Palindromes

string[] words = { "level", "world", "civic", "radar", "test" };

var query =
    from w in words
    let reversed = new string(w.Reverse().ToArray())
    where w == reversed
    select w;

foreach (var item in query)
    Console.WriteLine(item);

Output:

level
civic
radar

Here, let stores the reversed string so we can reuse it in the where clause.

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Why Use let?

• Reduce Repetition: Calculate once, reuse multiple times.
• Improve Readability: Makes queries easy to understand.
• Easier Maintenance: Change logic in one place.

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Quick Tip

let is different from into:

• let = temporary variable inside a query.
• into = continue querying a grouped or joined result.

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let is a small feature with a big impact. Start using it in your LINQ queries for cleaner and more efficient C# code.

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I’m Morteza Jangjoo and “Explaining things I wish someone had explained to me”