dcapwell commented on PR #2300:
URL: https://github.com/apache/cassandra/pull/2300#issuecomment-1529988979
I wonder why go down this route when we could offer a simpler solution.
yaml currently handles everything but validation/listeners, so could
decorate the `Properties` with a new validation and listener properties
```
public interface Listener<A, B>
{
default void onPreSet(A object, B value) {}
default void onPostSet(A object, B value) {}
}
public static class CompositeListener<A, B> implements Listener<A, B>
{
private final List<Listener<A, B>> listeners;
public CompositeListener(List<Listener<A, B>> listeners)
{
this.listeners = listeners;
}
@Override
public void onPreSet(A object, B value)
{
for (Listener<A, B> l : listeners)
l.onPreSet(object, value);
}
@Override
public void onPostSet(A object, B value)
{
for (Listener<A, B> l : listeners)
l.onPostSet(object, value);
}
}
public interface Validator<A, B> extends Listener<A, B>
{
void validate(B value);
default void validate(A object, B value)
{
validate(value);
}
@Override
default void onPreSet(A object, B value)
{
validate(object, value);
}
}
public static class ListenableProperty<A, B> extends ForwardingProperty
{
private final Listener<A, B> listener;
public ListenableProperty(String name, Property property,
Listener<A, B> listener)
{
super(name, property);
this.listener = listener;
}
@Override
public void set(Object o, Object o1) throws Exception
{
listener.onPreSet((A) o, (B) o1);
super.set(o, o1);
listener.onPostSet((A) o, (B) o1);
}
}
```
We need something to hold the `Map<String, Property>, so flexible where this
is, but feel like `DatabaseDescriptor` is likely the best place.
With this you only worry about `Property` and don't need to worry about
validation/notification as the property was decorated to add such capabilities
(and don't pay the cost to check this if nothing validates or listens)... We
also can set this up in `DatabaseDescriptor` so its immutable (we don't need
mutability with this), which mostly solves the mapping problem (as DD knows
everything, so can build this).
With this, we keep the logic small, 100% align with YAML (can't possibly
drift as YAML is what does the string mapping), and solve the "how does the
framework" know problem as we push this to `DatabaseDescriptor`, the place that
actually knows about this.
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