Can a C# lambda expression include more than one statement?
(Edit: As referenced in several of the answers below, this question originally asked about "lines" rather than "statements".)
- 19Yes, you can use multiple lines. I don't feel right making it a full answer.Tesserex– Tesserex2011-04-13 18:19:14 +00:00Commented Apr 13, 2011 at 18:19
- Good question. Yes, to have multiple statements after the arrow, you need to surround them with curly braces.Yster– Yster2023-06-19 10:34:37 +00:00Commented Jun 19, 2023 at 10:34
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9 Answers
Sure:
List<String> items = new List<string>(); var results = items.Where(i => { bool result; if (i == "THIS") result = true; else if (i == "THAT") result = true; else result = false; return result; } ); 
Comments
(I'm assuming you're really talking about multiple statements rather than multiple lines.)
You can use multiple statements in a lambda expression using braces, but only the syntax which doesn't use braces can be converted into an expression tree:
// Valid Func<int, int> a = x => x + 1; Func<int, int> b = x => { return x + 1; }; Expression<Func<int, int>> c = x => x + 1; // Invalid Expression<Func<int, int>> d = x => { return x + 1; }; 
2 Comments
Habeeb
I am trying to understand why Func allow braces and Expression is not allowing. Anyway Expression will complied as Func, Is there any way to add multiple line logic to Expression Tree? If no, Why there are restricting that?
Jon Skeet
@Habeeb: "Anyway Expression will complied as Func" Not always. A lot of the time it's never compiled to a delegate at all - just examined as data. Expression trees in .NET 4.0 did gain the ability to include multiple statements via Expression.Block but the C# language doesn't support that. It could, but that would require more design/implementation/test work.
You can put as many newlines as you want in a lambda expression; C# ignores newlines.
You probably meant to ask about multiple statements.
Multiple statements can be wrapped in braces.
See the documentation.
1 Comment
Tesserex
Wouldn't it be more accurate to say C# treats all whitespace, including newlines, equally? It sounds a bit misleading to say it ignores newlines - it makes it seem like it just strips them out completely, and you could split a keyword across a newline or something.
Func<string, bool> test = (name) => { if (name == "yes") return true; else return false; } 
2 Comments
asawyer
Func<string, bool> test = name => name=="yes";
Caius Jard
Polity is demonstrating the multi-line format requested by the question, not entertaining golfing suggestions. To implement your wise code would make it "not an answer"!
Since C# 7:
Single line statement:
int expr(int x, int y) => x + y + 1; Multiline statement:
int expr(int x, int y) { int z = 8; return x + y + z + 1; }; although these are called local functions I think this looks a bit cleaner than the following and is effectively the same
Func<int, int, int> a = (x, y) => x + y + 1; Func<int, int, int> b = (x, y) => { int z = 8; return x + y + z + 1; }; 
Comments
From Lambda Expressions (C# Programming Guide):
The body of a statement lambda can consist of any number of statements; however, in practice there are typically no more than two or three.
Comments
Another Example.
var iListOfNumbers = new List<int>() { 1, 2, 3, 4, 5 }; Func<List<int>, int> arithmeticSum = iList => { var finalResult = 0; foreach (var i in iList) finalResult = finalResult + i; return finalResult; }; Console.WriteLine(arithmeticSum.Invoke(iListOfNumbers)); Console.WriteLine(arithmeticSum(iListOfNumbers)); // The above two statements are exactly same. 
Comments
With c# 7.0 You can use like this also
Public string ParentMethod(int i, int x){ int calculation = (i*x); (string info, int result) InternalTuppleMethod(param1, param2) { var sum = (calculation + 5); return ("The calculation is", sum); } } 
Comments
Let say you have a class:
public class Point { public int X { get; set; } public int Y { get; set; } } With the C# 7.0 inside this class you can do it even without curly brackets:
Action<int, int> action = (x, y) => (_, _) = (X += x, Y += y); and
Action<int, int> action = (x, y) => _ = (X += x, Y += y); would be the same as:
Action<int, int> action = (x, y) => { X += x; Y += y; }; This also might be helpful if you need to write the a regular method or constructor in one line or when you need more then one statement/expression to be packed into one expression:
public void Action(int x, int y) => (_, _) = (X += x, Y += y); or
public void Action(int x, int y) => _ = (X += x, Y += y); or
public void Action(int x, int y) => (X, Y) = (X + x, Y + y); More about deconstruction of tuples in the documentation.
