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c#lambda
tronman
tronman

Reputation: 10125

Can a lambda expression be declared and invoked at the same time in C#?

In VB.NET, a lambda expression can be declared and invoked on the same line:

'Output 3
Console.WriteLine((Function(num As Integer) num + 1)(2))

Is this possible in C#?

Upvotes: 26

Views: 1582

Answers (4)

Servy
Servy

Reputation: 203828

Console.WriteLine(new Func<int, int>(i => i + 1)(2));

Uses a few less parentheses to use the Func's constructor than a cast.

Upvotes: 33

Jon Skeet
Jon Skeet

Reputation: 1501926

You have to tell the compiler a specific delegate type. For example, you could cast the lambda expression:

Console.WriteLine(((Func<int, int>)(x => x + 1))(2));

EDIT: Or yes, you can use a delegate creation expression as per Servy's answer:

Console.WriteLine(new Func<int, int>(i => i + 1)(2));

Note that this isn't really a normal constructor call - it's special syntax for delegate creation which looks like a regular constructor call. Still clever though :)

You can make it slightly cleaner with a helper class:

public static class Functions
{
    public static Func<T> Of<T>(Func<T> input)
    {
        return input;
    }

    public static Func<T1, TResult> Of<T1, TResult>
        (Func<T1, TResult> input)
    {
        return input;
    }

    public static Func<T1, T2, TResult> Of<T1, T2, TResult>
        (Func<T1, T2, TResult> input)
    {
        return input;
    }
}

... then:

Console.WriteLine(Functions.Of<int, int>(x => x + 1)(2));

Or:

Console.WriteLine(Functions.Of((int x) => x + 1)(2));

Upvotes: 44

Aidan
Aidan

Reputation: 4901

Kind or, you would have to use the Func object :

 var square = new Func<double, double>(d => d*d)(2);
 Console.WriteLine(square);

Upvotes: 1

Lance U. Matthews
Lance U. Matthews

Reputation: 16613

Yes, though it's messy:

Console.WriteLine(((Func<int, int>) (num => num + 1))(2));

Upvotes: 14

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