Question

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#?

Answer 1

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));