Expression Lambda versus Statement Lambda

Question

Fundamentally, is there any difference between a single-line expression lambda and a statement lambda? Take the following code, for example:

private delegate void MyDelegate();

protected static void Main()
{
    MyDelegate myDelegate1 = () => Console.WriteLine("Test 1");
    MyDelegate myDelegate2 = () => { Console.WriteLine("Test 2"); };

    myDelegate1();
    myDelegate2();

    Console.ReadKey();
}

While I prefer the first because I find the brackets to be ugly, is there anything different between the two (besides the obvious part about requiring brackets for multi-line statements)?

Stilgar · Accepted Answer · 2012-03-09 15:38:53Z

20

You need statement lambda for multistatement lambdas. In addition statement lambdas are not supported by expression providers like LINQ to SQL. Before .NET 4.0 the .NET Framework did not have support for statement expression trees. This was added in 4.0 but as far as I know no provider uses it.

Action myDelegate1 = () => Console.WriteLine("Test 1");
Expression<Action> myExpression = () => { Console.WriteLine("Test 2") }; //compile error unless you remove the { }
myDelegate1();
Action myDelegate2 = myExpression.Compile();
myDelegate2();

Otherwise they are the same.

edited Mar 9, 2012 at 15:38

answered Mar 9, 2012 at 15:22

Stilgar

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Comments

code4life · Accepted Answer · 2012-03-09 15:26:07Z

11

Reflector to the rescue! The disassembled code looks like this:

private static void Main(string[] args)
{
    MyDelegate myDelegate1 = delegate {
        Console.WriteLine("Test 1");
    };
    MyDelegate myDelegate2 = delegate {
        Console.WriteLine("Test 2");
    };
    myDelegate1();
    myDelegate2();
    Console.ReadKey();
}

So no, there is no real difference between the two. Be happy.

answered Mar 9, 2012 at 15:26

code4life

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Comments

Oded · Accepted Answer · 2012-03-09 15:20:09Z

8

The two are the same - the first is syntactic sugar to the second and both will compile to the same IL.

answered Mar 9, 2012 at 15:20

Oded

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Comments

Femaref · Accepted Answer · 2012-03-09 15:20:12Z

4

No, there is no difference in this example. If the body of the lambda is only one expression, you can drop the brackets. However, once the lambda contains more than one expression, like so:

MyDelegate myDelegate2 = () => { 
  Console.WriteLine("Test 2");                      
  Console.WriteLine("Test 2"); 
};

the brackets are mandatory.

answered Mar 9, 2012 at 15:20

Femaref

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kiss my armpit · Accepted Answer · 2014-08-18 17:38:48Z

4

If the delegate returns a value, return is necessary in statement lambda as follows.

        Func<int, int, bool> foo = (x, y) => { return x == y; };
        Func<int, int, bool> goo = (x, y) => x == y;

answered Aug 18, 2014 at 17:38

kiss my armpit

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1 Comment

Wappenull Over a year ago

Beside from multiple statements, presence of return keyword is also another fact. +1

Nicolas Tonneau · Accepted Answer · 2012-03-09 15:23:10Z

1

Personnaly, i prefer the Lambda Expression. The Expression have a value where the Statement does not.

i think the following links can help you :

http://lambda-the-ultimate.org/node/1044

answered Mar 9, 2012 at 15:23

Nicolas Tonneau

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Soner from The Ottoman Empire · Accepted Answer · 2016-09-18 14:28:10Z

0

Same for the OP example, but after C# 6.0, allowing you to use same expression syntax to define normal non-lambda methods within a class. For example:

public static double AreaOfTriangle(double itsbase, double itsheight)
{
    return itsbase * itsheight / 2;
}

The above code snippet can be written only if the method can be turned into a single expression. In short, it can be used the expression lambda syntax, but not the statement lambda syntax.

public static double 
              AreaOfTrianglex(double itsbase, double itsheight) => itsbase * itsheight / 2;

answered Sep 18, 2016 at 14:28

Soner from The Ottoman Empire

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Brucie Bruce · Accepted Answer · 2019-05-09 23:31:24Z

0

From the docs (https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/statements-expressions-operators/lambda-expressions):

Statement lambdas, like anonymous methods, cannot be used to create expression trees.

answered May 9, 2019 at 23:31

Brucie Bruce

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