If one designates a gift for another person, is it committed or can it be retracted?
I know that if one designates something for the temple (an offering or a donation), it can't be taken back -- it's committed. Is this a general principle of designating things, or is it specific to the temple (because designating it for the temple raises its holiness and we do not lower holiness)?
Suppose Reuven is out shopping, says "Shimon would like that; I will get it as a gift for him", and buys something. Is it now committed to Shimon, or may Reuven change his mind and keep it for himself? If he may not change his mind but Reuven discovers that Shimon can't use it (for example he remembers that Shimon is allergic to that food, or discovers that Shimon is out of town and the item is perishable), what happens?
I think I learned that for an animal that can't be offered, the temple sells it (and so benefits), but I don't know if it's practical for Shimon to sell a food gift he's allergic to. Does Reuven give it to him anyway and it's up to Shimon to re-gift it? For the case of Shimon not being available to receive the gift, the only temple parallel I can think of is items that were designated and not delivered before the destruction, but I don't know of any discussions of that case.