How does a free list work?

[Pavel Shkadzko]

I have been reading about memory management in D on 
https://wiki.dlang.org/Memory_Management and found an example of 
a free list (pattern?): "Free lists are a great way to accelerate 
access to a frequently allocated and discarded type.".

Here is the example of free list:
-----------------------------------------------
class Foo
{
     static Foo freelist; // start of free list
     Foo next; // for use by FooFreeList

     static Foo allocate()
     {
         Foo f;

	if (freelist)
         {
             f = freelist;
	    freelist = f.next;
	}
         else
	    f = new Foo();
	    return f;
     }

     static void deallocate(Foo f)
     {
	f.next = freelist;
	freelist = f;
     }
}
-----------------------------------------------

Do I understand correctly that by switching between static and 
non-static Foo we keep the object from being garbage collected by 
the GC? So in a situation when I need to create an object and 
then discard it, I can implement this pattern to use memory more 
efficiently.

Also, it's a little strange that since both f and freelist are 
null we are basically doing null = null in first if condition.