Unexpected language detail

Unexpected language detail

[James S. Rogers]

At work we were designing a generic bounded queue package
indexed by a modular type.  One of our requirements for this queue
package is that it be able to correctly work with any modular type
as the index.

We encountered a problem when the queue contained a single
element.  This condition occurs when someone instantiates the
package with a type defined as

type Index is mod 1;

Of course, the only valid value in this type is 0.  The iterator for a
queue with this type cannot use arithmetic.  You cannot add 1 to
the current value to get 0 because 1 is out of the range of the type.

The solution we found was to use the 'SUCC attribute for the index
type.  This produced a correct iterator for all possible modular index
types.

Jim Rogers
Colorado Springs, Colorado