@Target(value=ANNOTATION_TYPE) @Retention(value=RUNTIME) public @interface MonotonicQualifier
Tto another qualifier
S. The annotation
Sis called the target of the monotonic qualifier, and has to be indicated by
This meta-annotation can be used on the declaration of the monotonic qualifier used for the
type-system at hand, and is often called
MonoT if the target is
T. The subtyping
hierarchy has to be defined as follows:
T <: MonoT <: S
<:indicates the subtyping relation.
An expression of a monotonic type can only be assigned expressions of the target type
T. This means that an expression of the monotonic type
MonoT cannot be assigned to a
variable of the same type.
Reading an expression of a monotonic type
MonoT might always yield an expression of
S. However, once it has been observed that a variable has the target type
the monotonic property ensures that it will stay of type
T for the rest of the program
execution. This is even true if arbitrary other code is executed.
Note that variables of a monotonic type can be re-assigned arbitrarily often, but only with expressions of the target type.