Queue push/pop

[David Hopwood]

Brian Rice wrote:
> On Jan 4, 2006, at 3:41 AM, Tony Garnock-Jones wrote:
> 
>> (triggered by the changes to the process code to use push/pop  instead of
>> addLast/removeFirst)
>>
>> I don't like these names. Push and pop to me mean stack-like, LIFO
>> behaviour. Using them to mean FIFO behaviour seems weird.
> 
> These are used in standard textbooks for FIFO protocol, and we use  the
> polymorphism in TraversalStream to shift between depth-first and 
> breadth-first traversals, so I think it's fair to say that we're 
> getting a benefit from the polymorphism. Also, LIFO and FIFO are not 
> the only possible animals where push:/pop are suitable protocols,  like
> Heap's push:/pop which obey a sorting setup.
> 
> It's weird, but on the other hand it's tedious to have code that has  to
> indicate where first/last interplay in an explicit way. After all,  it
> doesn't matter which is first and which is last, only that there  is
> FIFO semantics, in the same way that we don't really care that  Stack is
> a Sequence whose "active" end is the "last"-word end of it.
> 
> We can always add queries to indicate whether something is a LIFO or FIFO.

I would suggest leaving {push,pop} as they are now (with the latest change),
and also supporting {addLast,addFirst,removeLast,removeFirst}.

The allows the correct intent to be expressed for any given client: in some
cases the intent is to push and pop without any dependency on order, and in
others the order matters.

-- 
David Hopwood <david.nospam.hopwood at blueyonder.co.uk>