C#: Returning 'this' for method nesting?

Question

I have a class that I have to call one or two methods a lot of times after each other. The methods currently return void. I was thinking, would it be better to have it return this, so that the methods could be nested? or is that considerd very very very bad? or if bad, would it be better if it returned a new object of the same type? Or what do you think? As an example I have created three versions of an adder class:

// Regular
class Adder
{
    public Adder() { Number = 0; }

    public int Number { get; private set; }

    public void Add(int i) { Number += i; }
    public void Remove(int i) { Number -= i; }
}

// Returning this
class Adder
{
    public Adder() { Number = 0; }

    public int Number { get; private set; }

    public Adder Add(int i) { Number += i; return this; }
    public Adder Remove(int i) { Number -= i; return this; }
}

// Returning new
class Adder
{
    public Adder() : this(0) { }
    private Adder(int i) { Number = i; }

    public int Number { get; private set; }

    public Adder Add(int i) { return new Adder(Number + i); }
    public Adder Remove(int i) { return new Adder(Number - i); }
}

The first one can be used this way:

    var a = new Adder();
    a.Add(4);
    a.Remove(1);
    a.Add(7);
    a.Remove(3);

The other two can be used this way:

    var a = new Adder()
        .Add(4)
        .Remove(1)
        .Add(7)
        .Remove(3);

Where the only difference is that a in the first case is the new Adder() while in the latter it is the result of the last method.

The first I find that quickly become... annoying to write over and over again. So I would like to use one of the other versions.

The third works kind of like many other methods, like many String methods and IEnumerable extension methods. I guess that has its positive side in that you can do things like var a = new Adder(); var b = a.Add(5); and then have one that was 0 and one that was 5. But at the same time, isn't it a bit expensive to create new objects all the time? And when will the first object die? When the first method returns kind of? Or?

Anyways, I like the one that returns this and think I will use that, but I am very curious to know what others think about this case. And what is considered best practice.

Answer 1

The 'return this' style is sometimes called a fluent interface and is a common practice.