`this` and a class constructor

Question

I currently have a class and I am a bit confused with its constructor .

 public class BarListTracker : GotTickIndicator
 {
    public BarListTracker(BarInterval interval) : this(new BarInterval[] { interval }) { }
 }

what does the statement this(new BarInterval[] { interval }) imply ?

Answer 1

This is constructor chaining. Essentially, you're calling a different constructor before executing the contents of that constructor.

public class Foo
{
    public Foo()
        : this("Hello")
    {
        Console.Write(" World!");
    }

    public Foo(string text)
    {
        Console.Write(text);
    }
}

new Foo(); //outputs "Hello World!"

So somewhere in your BarListTracker there should be another constructor that takes either a BarInterval[] array or an IEnumerable<BarInterval> like this:

public class BarListTracker : GotTickIndicator
{
    public BarListTracker(BarInterval interval) 
        : this(new BarInterval[] { interval }) 
    { 
        //specific initialization for this constructor
    }

    public BarListTracker(BarInterval[] intervals) 
    { 
        //shared initialization logic for both constructors
    }
}

It will execute the body BarListTracker(BarInterval[]), then execute the body of BarListTracker(BarInterval)

This is generally used to reduce code duplication. If you had some initialization code for your BarListTracker, it makes more sense to write it in one place and share that logic with your constructors rather than rewriting it for each one.

In addition, it lets you pass in or modify the input parameters with basic expressions. So in this case, in-line with calling the BarListTracker(BarInterval[]) constructor, it's wrapping the single BarInterval interval object as an array to match the signature. Likely this is just a convenience overload to provide a simpler API for programmers who may often have only a single BarInterval to construct the tracker with.

Answer 2

This means a call of another constructor of the BarListTracker that takes an array of BarInterval objects, passing in an array containing the object passed into this constructor. It makes the call

var tracker = new BarListTracker(interval);

equivalent to this:

var tracker = new BarListTracker(new BarInterval[] { interval });