import java.lang.invoke.*;

public class AlmostFinal<T> {
	private final MethodHandle getter;
	private SwitchPoint switchPoint;
	private VolatileCallSite callSite;
	
	public AlmostFinal(T initial) {
		switchPoint = new SwitchPoint();
		callSite = new VolatileCallSite(MethodType.genericMethodType(0));
		getter = switchPoint.guardWithTest(MethodHandles.constant(Object.class, initial), callSite.dynamicInvoker());
	}
	
	public T value() {
		try {
			return (T) getter.invokeExact();
		} catch (Throwable t) {
			throw new Error(t); // Shouldn't happen
		}
	}
	
	public synchronized void setValue(T val) {
		final SwitchPoint[] invalid = { switchPoint };
		switchPoint = new SwitchPoint();
		final VolatileCallSite previousSite = callSite;
		callSite = new VolatileCallSite(MethodType.genericMethodType(0));
		previousSite.setTarget(switchPoint.guardWithTest(MethodHandles.constant(Object.class, val), callSite.dynamicInvoker()));
		SwitchPoint.invalidateAll(invalid);
	}
}