又学到了新知识点😄tuple struct可以直接作为函数使用

--
👇
whfuyn: ``` #[stable(feature = "rust1", since = "1.0.0")] pub struct TcpListener(net_imp::TcpListener);

这个是`TcpListener`的定义，它在这里被用作构造函数。

我没找到哪里有说`tuple struct`的`constructor`实现了`FnOnce`，不过这里有一段可以看一下：

https://doc.rust-lang.org/stable/reference/expressions/struct-expr.html

Tuple struct expression

A struct expression with fields enclosed in parentheses constructs a tuple struct. 
Though it is listed here as a specific expression for completeness, it is equivalent to a call expression to the tuple struct's constructor. 

#[stable(feature = "rust1", since = "1.0.0")]
pub struct TcpListener(net_imp::TcpListener);

这个是TcpListener的定义，它在这里被用作构造函数。

我没找到哪里有说tuple struct的constructor实现了FnOnce，不过这里有一段可以看一下：

https://doc.rust-lang.org/stable/reference/expressions/struct-expr.html

Tuple struct expression

A struct expression with fields enclosed in parentheses constructs a tuple struct. Though it is listed here as a specific expression for completeness, it is equivalent to a call expression to the tuple struct's constructor.

因为TcpListener的类型是struct TcpListener(net_imp::TcpListener);，所以你就把它名字当成构造函数理解就完了。具体在Rust里面这叫什么概念我也忘了。