What's the meaning of "=>" in C#?

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C# Lambda ( => )

For instance

Messenger.Default.Register<AboutToCloseMessage>(this, (msg) =>
        {
            if (msg.TheContainer == this.MyContainer) // only care if my container.
            {
                // decide whether or not we should cancel the Close
                if (!(this.MyContainer.CanIClose))
                {
                    msg.Execute(true); // indicate Cancel status via msg callback.
                }
            }
        });

@Shakti Singh: Can you show us how to search for the `=>` symbol? — BoltClock, Jun 08 '11 at 13:19
@Shakti Singh: If Rdeluca knew `=>` means "lambda expression" he wouldn't be asking in the first place. — BoltClock, Jun 08 '11 at 13:24
Yeah.. Had no idea it was called lambda or I would've searched it. Thanks! — Rdeluca, Jun 08 '11 at 13:46

score 2 · Answer 1 · answered Jun 08 '11 at 13:18

2

The

=>

Operator is used for Lambda Expressions.

http://msdn.microsoft.com/en-us/library/bb397687.aspx

It allows you to define an anonymous function "on the fly" and can be used to create delegates or expression tree types.

answered Jun 08 '11 at 13:18

invalidsyntax

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score 1 · Accepted Answer · answered Jun 08 '11 at 13:21

It is a lambda, it allows you to create a function easily.

in your example you can also write:

Messenger.Default.Register<AboutToCloseMessage>(this, delegate(Message msg)
{
    if (msg.TheContainer == this.MyContainer) // only care if my container.
    {
        // decide whether or not we should cancel the Close
        if (!(this.MyContainer.CanIClose))
        {
            msg.Execute(true); // indicate Cancel status via msg callback.
        }
    }
});

or even

Messenger.Default.Register<AboutToCloseMessage>(this, foobar);

// somewhere after //
private void foobar(Message msg)
{
    if (msg.TheContainer == this.MyContainer) // only care if my container.
    {
        // decide whether or not we should cancel the Close
        if (!(this.MyContainer.CanIClose))
        {
            msg.Execute(true); // indicate Cancel status via msg callback.
        }
    }
}

score 0 · Answer 3 · answered Jun 08 '11 at 13:18

0

It's a lambda expression (http://msdn.microsoft.com/en-us/library/bb397687.aspx).

answered Jun 08 '11 at 13:18

Achim

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score 0 · Answer 4 · answered Jun 08 '11 at 13:19

0

its a lamda expression (Function Argument ) => { Function Body}

The type of the argument can be specified but the complier will generally just interpret it.

answered Jun 08 '11 at 13:19

rerun

25,014
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score 0 · Answer 5 · answered Jun 08 '11 at 13:19

That is how you define lambda in C#. msg is the argument, passed to the lambda method, and the rest is the body of the method.

The equivalent of that is this:

Messenger.Default.Register<AboutToCloseMessage>(this, SomeMethod);

void SomeMethod(SomeType msg)
{
    if (msg.TheContainer == this.MyContainer) // only care if my container.
    {
        // decide whether or not we should cancel the Close
        if (!(this.MyContainer.CanIClose))
        {
             msg.Execute(true); // indicate Cancel status via msg callback.
        }
    }
}

What's the meaning of "=>" in C#?

5 Answers5