Question about delegates

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I thought I understood delegates, but I clearly don't since this code gives me output different than I was expecting. Why doesn't the invoke throw a NullRefenceException after we assign speaker to null or to a new instance? Is it because the garbage collector has not had a chance to clean things up?

What I have tried:

C#

void Main()
{
	var speaker = new Speaker();
	Action action = new Action(speaker.SayName);
	
	speaker.Name = "Luke";
	action.Invoke(); // outputs "My name is Luke"
	
	speaker.Name = "Leia";
	action.Invoke(); // outputs "My name is Leia"
	
	speaker = null;
	action.Invoke(); // outputs "My name is Leia"
	
	speaker = new Speaker();
	speaker.Name = "Chewy";
	action.Invoke(); // outputs "My name is Leia"
}


class Speaker
{
	public string Name { get; set; }
	
	public void SayName()
	{
		Console.WriteLine($"My name is {Name}");
	}
}

Posted 4-Sep-20 2:42am

TheRedEye

Updated 4-Sep-20 2:53am

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F-ES Sitecore · Accepted Answer · 2020-09-04T02:53:00

C#

// this creates a Speaker object in memory (let's say at address 10000)
// and creates a speaker variable that references that object (at address 10000)
var speaker = new Speaker();
// This creates an Action with a target that is the SayName method on the object
// at memory address 10000
Action action = new Action(speaker.SayName);

// ...

// this stops speaker pointing to memory address 10000 but the
// object at 10000 (the Speaker object) still exists, so the SayName
// method that Action is referencing also still exists
speaker = null;
// this does what it always has done, calls SayName on the object at address 10000
action.Invoke(); // outputs "My name is Leia"

// setting a variable to null only destroys that object (during GC) if nothing else
// is referencing that object.  However as the Action is referencing the
// object at address 10000 it is not destroyed.