The Rambam writes [Laws of Vows 12 law 10] that ''If a wife  says 'my hands are holy to he who made them' or took a vow that her husband should not derive any benefit from the work of her hands her husband is not forbidden in the work of her hands because that work is under obligation to him. ...but he must revoke her vow because he might divorce her and then be forbidden  to remarry her.'' The Ran asks [Ketuboth 59] that that should be only in the case she said ''her hands will be holy to he who made them'' but not when she forbids the work of her hands because that work has not yet come into existence and so the vow does not apply to them  at all. And the Kesef Mishna says that the Rambam is going like Rav Ashi that holiness of body does apply even to things not yet in existence. Rav Shach uses that same answer for a similar question. But this answer is contradicted by Rambam Laws of Buying 22 laws 15 and 16. There he writes ''If a man says ''what my animal gives birth to will be holy for the temple or will be forbidden to me or I will give it to charity,'' even though it does not become holy , still he has to fulfill what he said'' and when he said ''will be forbidden to me'' that is a vow which is in the category of holiness of body. 

The place where Rav Shach uses that answer of the Kesef Mishna is in in Rambam Laws of Sale 22 law 9.  But that answer is going on Rambam Laws of the Second Tithe 9 law 7. ''Modest people  would leave money in the year of shemita and say 'anything taken from the fruits of the fourth year that holiness is settled on this money'. The question there is the fruits are not in the possession of the owner, but of him who picked them.  

 I might mention that a vow comes from the law about sacrifices. One who says 'this bread is like a sacrifice to me' is forbidden to eat it.

To answer this question on the Rambam and the answer of Rav Shach one needs to look at Rambam Laws of Meila 4 halacha 9 where the Rambam holds one is obligated for a sacrifice of meila only when he said this object will be forbidden to me like a sacrifice. But if he did not say ''like a sacrifice'', he is not obligated. Thus in cases up above where the Rambam says the vow or money can be '''chal' even on something not yet in existence that must be where he or she said ''like a sacrifice.''