eat one's cake and have it too

[eat one's cake and have it too] {v. phr.} To use or spendsomething and still keep it; have both when you must choose one of twothings. Often used in negative sentences.

Roger can't make up hismind whether to go to college or get a job. You can't eat your cakeand have it too.

Mary wants to buy a beautiful dress she saw atthe store, but she also wants to save her birthday money for camp. Shewants to eat her cake and have it too.