Question

Here is the code:

class Class1
{    
    private Class2 object;

    public Class1(Class2 obj) : this(obj.ToString())
    {
        this.object = obj;
    }
}

More specifically, what does the : this part do.

Answer 1

The :this(obj.ToString) causes the constructor code for the constructor defined taking a string parameter to run first. Once it runs, then the constructor code (setting this.object = obj) is executed.

This is covered in MSDN’s page on Constructors (the last example set).

Note that, in your code above, as written, this will cause a compiler error. You would also need to have a constructor like the following:

public Class1(string str) // Constructor taking a string, though it could be non-public
{
    // Do something with str
}

With this constructor in place, it will get called, perform it’s initialization steps, then the first constructor (which sets this.object) will run.