Often I will encounter the use of - or even use myself - the value
-1 as an edge case in otherwise integer data structures. For instance, as the value for "irreplaceable" in a Replacement Cost field.
This is especially useful where
null is either unrecognised; semantically overburdened; or converted into
empty when migrating data across formats.
What is the formal computer science view on the use of negative integers for non-numeral meanings in data fields which are still used normally for positive integers?