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

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)); 

Answer 2

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

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