You have several ways of getting an interface object.

The implicit way has the advantage in that the compiler makes sure that the interface is implemented by the class. The disadvantage is that someone reading your code won't know that this is an interface being torn off. This just might need some more comments, that's it.

The explicit way has the advantage in that you have exactly called out the interface name. The problem is that you won't find out until runtime whether the code actually works or not. An exception will be thrown if the conversion is not able to take place.

The explicit way with the "as" has the advantage of being able to check if the interface is implemented similar to what was discussed above. Keep in mind that when you use the "as" method then you should be checking for null.

static void Main()
{
    Tester    tst = new Tester();
    IReader  reader;

    // implicit compile-time conversion
    reader = tst; 
    
    // explicit run-time conversion with exception
    reader = (IReader)tst;

    // explicit run-time conversion with null
    reader = tst as IReader;
}