C# – Meaning of () => Operator

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I read this interesting line here, in an answer by Jon Skeet.

The interesting line is this, where he advocated using a delegate:

Log.Info("I did something: {0}", () => action.GenerateDescription());

Question is, what is this ()=> operator, I wonder? I tried Googling it but since it's made of symbols Google couldn't be of much help, really. Did I embarrassingly miss something here?

Best Answer

This introduces a lambda function (anonymous delegate) with no parameters, it's equivalent to and basically short-hand for:

delegate void () { return action.GenerateDescription(); }

You can also add parameters, so:

(a, b) => a + b

This is roughly equivalent to:

delegate int (int a, int b) { return a + b; }

Related Solutions

C# – What Does the ‘=>’ Syntax Mean?

It's the lambda operator.

From C# 3 to C# 5, this was only used for lambda expressions. These are basically a shorter form of the anonymous methods introduced in C# 2, but can also be converted into expression trees.

As an example:

Func<Person, string> nameProjection = p => p.Name;

is equivalent to:

Func<Person, string> nameProjection = delegate (Person p) { return p.Name; };

In both cases you're creating a delegate with a Person parameter, returning that person's name (as a string).

In C# 6 the same syntax is used for expression-bodied members, e.g.

// Expression-bodied property
public int IsValid => name != null && id != -1;

// Expression-bodied method
public int GetHashCode() => id.GetHashCode();

C# – What Does the Operator ‘=>’ Mean?

Basically it's specifying an anonymous function, that takes no parameters that calls SomeAction. So yes, they are functionally equivalent. Though not equal. Using the lambda is more equivalent to:

del = new SomeDelegate(this.CallSomeAction);

where CallSomeAction is defined as:

public void CallSomeAction()
{
    this.SomeAction();
}

Hope that helps!

Best Answer

Related Solutions

C# – What Does the ‘=>’ Syntax Mean?

C# – What Does the Operator ‘=>’ Mean?

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