It would be very nice.
You could have done it yourself. (省略If you had wanted to.上下文可以看出You didn’t want to.) (Fact: You didn’t do the work yourself because you didn’t want to.)
I wouldn’t smoke. (省略If I were you.) (表面上说我，实际上说你。这是一种委婉的表达法。（Fact: You smoke very often. I advise you not to smoke any more.）
2）省略主句：在强调条件从句时，常省略主句，这种句子常表示一种“已不能实现”的愿望，主要用于If only 引导的感叹句中。
If only he were here!
If only I knew more!
If only he had stayed with us!
1.If only I had taken his advice!
2.If only I were a bird.
3.If only I could live in a big apartment!
4.If only I were a billionaire!
5.If only I could marry her/him!