Question

It’s+adj+of/for+sb to do sth如何还原成不带形式主语it？

比如
It's impolite of you to visit someone without telling him in advance
是否可还原成
To visit someone without telling him in advance is impolite of you
还有
It's really difficult for me to learn dancing
是否可还原成
To learn dancing is really difficult for me

Answer 1

为您解答
Of,for这两句都属于不定式的复合结构。
不定式前的形容词描述的是不定式逻辑主语的性质、身份、特征时，该逻辑主语用of 引出。这时，逻辑主语与前面的形容词构成主表关系。所以是这么改:
It's impolite of you to visit someone without telling him in advance=You are impolite to visit someone without telling him in advance

追答

It's really difficult for me to learn dancing
可还原成For me to learn dancing is really difficult
不定式复合结构不要拆分

Answer 2

直接用sb做主语，主系表结构就OK了

追答

按理说最好不还原，因为这个用法更高级，并且有些adj.在sb直接为主语时+be+adj时不太常见