Func and Action

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Func provides a holder for parameterised anonymous functions. The leading types are the inputs and the last type is always the return value.

// square a number.
Func<double, double> square = (x) => { return x * x; };

// get the square root.
// note how the signature matches the built in method.
Func<double, double> squareroot = Math.Sqrt;

// provide your workings.
Func<double, double, string> workings = (x, y) => 
    string.Format("The square of {0} is {1}.", x, square(y))

Action objects are like void methods so they only have an input type. No result is placed on the evaluation stack.

// right-angled triangle.
class Triangle
    public double a;
    public double b;
    public double h;

// Pythagorean theorem.
Action<Triangle> pythagoras = (x) => 
    x.h = squareroot(square(x.a) + square(x.b));

Triangle t = new Triangle { a = 3, b = 4 };
Console.WriteLine(t.h); // 5.

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