Question

Can you please tell me what kind of construct in C# is this.

Code Golf: Numeric equivalent of an Excel column name

C.WriteLine(C.ReadLine() 
            .Reverse() 
            .Select((c, i) => (c - 64) * System.Math.Pow(26, i)) 
            .Sum());

Though I am new to C# (only two months exp so far), but since the time I have joined a C# team, I have never seen this kind of chaining. It really attracted me and I want to learn more about it.

Please give some insight about this.

Answer 1

Method chaining like this is often called a fluent interface.

You can make your own fluent interface by implementing functions that return the object they were called on.

For a trivial example:

class Foo 
{
    private int bar;

    public Foo AddBar(int b) 
    {
        bar += b;
        return this;
    }
}

Which can be used like:

Foo f = new Foo().AddBar(1).AddBar(2);

You could also implement a fluent interface using extension methods.

For example:

class Foo 
{
    public int Bar { get; set; }
}

static class FooExtensions 
{
    public static Foo AddBar(this Foo foo, int b)
    {
        foo.Bar += b;
        return foo;
    }
}

etc.

Here is a more complex example. Finally, Autofac and CuttingEdge.Conditons are two examples of open-source libraries that have very nice fluent interfaces.