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Short answer

To create a lambda expression, specify input parameters (if any) on the left side of the lambda operator and an expression or a statement block on the other side. (S1) Lambdas are usually assigned to delegate types such as Func<> and Action<>, which are type-safe references to methods. [S1][S2]

Func<int, int> square = x => x * x;
Action<string> log = msg => { Console.WriteLine(msg); };

Key points

• Delegates let you pass methods as arguments, and event handlers are invoked through them. [S2]
• Assigned to Expression<Func<...>>, a lambda becomes an expression tree instead of code (used by LINQ providers). [S1]

Claims

• id: C1 claim: The => operator separates a lambda's parameters from its body. source: S1 evidence: "Use the lambda declaration operator => to separate the lambda's parameter list from its body."
• id: C2 claim: A lambda can be assigned to a Func delegate. source: S1 evidence: "Func<int, int> square = x => x * x;"
• id: C3 claim: A delegate represents references to methods with a given signature. source: S2 evidence: "A delegate is a type that represents references to methods"
• id: C4 claim: Delegates pass methods as arguments to other methods. source: S2 evidence: "Delegates are used to pass methods as arguments to other methods."

Sources

• [S1] Lambda expressions - Lambda expressions and anonymous functions - C# reference. Microsoft Learn (.NET docs). https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/lambda-expressions . License: CC BY 4.0 (dotnet/docs). Accessed 2026-11-04.
• [S2] Work with delegate types in C# - C#. Microsoft Learn (.NET docs). https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/delegates/ . License: CC BY 4.0 (dotnet/docs). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_0qswyhpx,
  author = {{iinventedlight}},
  title = {{C\# lambda expressions and delegates}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/csharp-lambda-expressions/},
  note = {Permanent ID iil:note:0qswyhpx. License: CC-BY-4.0.},
}

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