Catching up on email...
On 1/10/2020 1:43 PM, Brian Goetz wrote:
[snip]
- annotation types can't directly contain things prohibited in
interfaces, or instance/local methods (maybe)
- currently annos cannot have fields, default methods, or static
methods -- this still seems a reasonable restriction.
Why? I mean, I don't really care all that much, but if we're removing
ad hoc restrictions, this one (no methods) certainly seems ad hoc. We
don't even need new syntax.
Because annotations are supposed to be pure metadata. These things
all pull state and behavior into something that is supposed to be pure
metadata. I mean, sure, I can imagine a world that blurs the
distinction between annotations and interfaces, but I'm not seeing
these restrictions as _gratuitous_; they were made deliberately.
The design center of usage of annotations assumes the identity of Class
objects can be used to distinguish different annotation types via
AnnotatedElement.getAnnotation(Class<T> annotationClass). In a class
file, an annotation type is identified by name and a runtime lookup
occurs to convert the name to a class object. A known limitation of the
API is the absence of a mechanism to provide a class loader to mediate
this lookup (JDK-6537080). This may interact with plans to remove nested
restrictions on annotation types.
HTH,
-Joe
