关于宾语补足语

我觉得不是宾补,更像是动词不定式做主语,句子可以改为:
To wash it is my turn
只不过英语里习惯于动词不定式做主语时后置,把it放在句首来代替动词不定式做主语而已.
类似的句子还有:
It is a good idea to go on a picnic
It's my pleasure to do sth

我也没搞懂!对不起啦!