TLinkedList Iterator usage

Hi,
why this two lines of code do not give an error:

    TMap<float, float > mymap;
    TMap<float, float >::TIterator it(mymap);

While these two give an error on the second line while trying to compile?

    TLinkedList< float> test;
    TLinkedList< float >::TIterator it(test);

Error is: