Bug or a game rule?

[gecslam]

I'm not sure if this is a bug or an actual rule. I'm implementing the card Covetous Dragon from Urza's Destiny, which sacrifices when you control no artifacts. How does a card like this interact with flicker effects like Momentary Blink and Cloudshift? Say I cast either of those on my only artifact in play: for the brief second that that card is exiled, would I need to sac Covetous Dragon? I've implemented the rule as a triggered ability and have it working for obvious cases, but it's not working if I test it with a flicker effect.

[LevelX]

Probably a bug in implemenation of StateTriggeredAbilities.
I will have a look later.

603.8. Some triggered abilities trigger when a game state (such as a player controlling no permanents of a particular card type) is true, rather than triggering when an event occurs. These abilities trigger as soon as the game state matches the condition. They’ll go onto the stack at the next available opportunity. These are called state triggers. (Note that state triggers aren’t the same as state-based actions.) A state-triggered ability doesn’t trigger again until the ability has resolved, has been countered, or has otherwise left the stack. Then, if the object with the ability is still in the same zone and the game state still matches its trigger condition, the ability will trigger again.

Example: A permanent’s ability reads, “Whenever you have no cards in hand, draw a card.” If its controller plays the last card from his or her hand, the ability will trigger once and won’t trigger again until it has resolved. If its controller casts a spell that reads “Discard your hand, then draw that many cards,” the ability will trigger during the spell’s resolution because the player’s hand was momentarily empty.

[emerald000]

I'm not sure if this is a bug or an actual rule. I'm implementing the card Covetous Dragon from Urza's Destiny, which sacrifices when you control no artifacts. How does a card like this interact with flicker effects like Momentary Blink and Cloudshift? Say I cast either of those on my only artifact in play: for the brief second that that card is exiled, would I need to sac Covetous Dragon? I've implemented the rule as a triggered ability and have it working for obvious cases, but it's not working if I test it with a flicker effect.

You should use a StateTriggeredAbility. It is quite possible that there is a bug with blink effects though.

[gecslam]

You should use a StateTriggeredAbility. It is quite possible that there is a bug with blink effects though.

That's how I did it, and the flicker effect still doesn't work properly. I stepped through, and it looks like the card that gets flickered moves to exile and back to the battlefield before the GameEvent notifying the first zone change gets sent (for some reason, the moveToExile() method in CardImpl delays firing the event notice until later, but fires the event immediately in putOntoTheBattlefield()). So when the first zone change event fires, and my TriggeredAbility implementation checks the battlefield for artifact permanents, the artifact is already back in play. I'll add this info to the Issues page on Github.