This package lets you create an array which will allow only one
occurrence of any value. In other words, no matter how many times
you put in 42 it will keep only the first occurrence and the rest
will be dropped. You use the module via tie and once you tied your
array to this module it will behave correctly.
Uniqueness is checked with the 'eq' operator so among other things
it is case sensitive. As a side effect the module does not allow
undef as a value in the array.
