static void Main(string[] args)
{
var b = new ObjectB();
var a = new ObjectA(b);
a.DoStuff();
}
static void Main(string[] args)
{
//var b = new ObjectB();
var b = new BetterObjectB();
var a = new ObjectA(b);
// we were able to change the behavior of the program (and specifically ObjectA) without modifying A's code (Open/Close principle / De-coupling).
// this can be extremely powerful, especially with multiple developers / teams / third party libraries.
// sometimes you can't edit ObjectA, but you can supply a BetterObjectB.
a.DoStuff();
}