such as 中as是连词还是介词?Such a clever boy as he can learn anything quickly.这个句子中as是什么词性?

连词
（一）、 as作连词的用法:
1.作“在-------期间,当----的时候”引导时间状语从句.注意与when、 while的用法区别.
①下列情形时,只用as,而不用when或while.
1)用于表示同一个人的两种动作交替进行,指一边----一边.如:
The girl sings as she goes to school.
He looked behind occasionally as he went forward in the forest.
2)表示两个同步发生的动作或行?意思是随着-----的发展.如:
As time went on / by,she became more and more beautiful .
As children get older,they become more and more interested in everything.
3)表示两个短暂行为或事情几乎同时发生.如:I watched her as she read the book.
I thought of it just as you opened your mouth.
Just as the flying worm hit her face,she gave a loud cry.
4)接在名词后面表示某一个年龄段时.如:
As a young man,he was active in sports.
②when作"当……的时候"解,可以指较短的(一点)时间,也可指一段时间.如:When I was at college,I could speak several foreign languages.When the clock struck twelve,I had slept for 2hours.
③ while常表示一段较长的时间或一个过程,强调主句谓语动词与从句谓语动词同时发生.如:Work while you work.Play while you play.
2.As =Since 作"既然"、"由于"解,引导原因状语从句,常用来表示已为人们所知或显而易见的原因或理由.如:As he’s been ill for ages,I will help him.
As / Since you're not feeling well,you may stay at home.
As he wasn't ready ,we went without him.
3.As =in the way that作"像"、"按照……的方式"解,引导方式状语从句.如:
Do as I told you.
Remember,you must do everything as I do.
4.用于as--- as或not / so/ as ---- as中,前一个as是副词,后一个as是连词,引导比较状语从句.如:They helped the old as much as possible.
I don't speak English so/ as well as she does.
5.表示虽然,尽管 等,引导让步状语从句,常用倒装语序,模式为:
adj./adv./ n.+as +主语+谓语+主句.如:Young as he is,he knows much.
Tired as they were,they walked on.
6.表示也------一样.She is a doctor,as was her husband.
（二）、 as作关系代词,引导定语从句,表示正如,这一点.如:
He is very careful,as we all know.
As is well-known,* belongs to China.
另外,当先行词被the same,such等词修饰时,常用as来引导定语从句.如:
{{{{Such a clever girl as she can learn anything quickly.
I was reading the same book as he bought yesterday.}}}}