question as to when a new command gets executed

[WhatMeWorry]

I've been studying an 8 year old D project in Github and this 
code fragment has left me befuddled. I'm confused as to when and 
how the new BreakState() statement gets executed. Wouldn't the 
class DebuggerSession need to be instantiated first and then the 
this() constructor be called?  Which begs the question, how would 
the statement, m_State = new BreakState() ever get executed?

class DebuggerSession
{
     private BreakState m_State = new BreakState();
     private UnrealCallback m_UnrealCallback;

     this( )
     {
     }
     // rest of class
}