Function tao_of_rust::ch05::share_mutable::lexical_scope

pub fn lexical_scope()

词法作用域和生命周期

Base usage: let 绑定会创造词法作用域

fn main(){
    let a = "hello";   // -------scope a-------+
    let b = "rust";    // -----scope b------+  |
    let c = "world";   // ---scope c ----+  |  |
    let d = c;         // - scope d ---  |  |  |
} //----------------------------------+--+--+--+

Base usage: 花括号创造词法作用域

fn main(){
    let outer_val = 1;
    let outer_sp = "hello".to_string();
    {
        let inner_val = 2;
        outer_val;
        outer_sp;
    }
    println!("{:?}", outer_val);
    // error[E0425]: cannot find value `inner_val` in this scope
    // println!("{:?}", inner_val);
    // error[E0382]: use of moved value: `outer_sp`
    // println!("{:?}", outer_sp);
}

Base usage: match匹配的花括号创造词法作用域

fn main(){
    let a = Some("hello".to_string());
    match a { // ------------------------------
        Some(s) => println!("{:?}", s),      // | match scope
        _ => println!("nothing")              // |
   } // --------------------------------------
   // error[E0382]: use of partially moved value: `a`
   // println!("{:?}", a);
}

Base usage: 循环表达式花括号创造词法作用域

fn main(){
    let v = vec![1,2,3];
    for i in v { // ------------------------------------
        println!("{:?}", i);                             // |
        // error[E0382]: use of moved value: `v`     // | for scope
        //  println!("{:?}", v);                         // |
    }  //-----------------------------------------------
}

Base usage: if let表达式花括号创造词法作用域

fn main(){
    let a = Some("hello".to_string());
    if let Some(s) = a { // -------
        println!("{:?}", s)       //|  if let scope
    } //---------------------------
}

Base usage: while let表达式花括号创造词法作用域

fn main() {
    let mut optional = Some(0);
    while let Some(i) = optional { // ------------------ ----+
        if i > 9 {                                   //      |
            println!("Greater than 9, quit!");       //      |
            optional = None;                         //      |
        } else {                                     //      |  while scope
            println!("`i` is `{:?}`. Try again.", i);//      |
            optional = Some(i + 1);                  //      |
       }                                             //      |
    } // ----------------------------------------------------+
}

Base usage: 函数花括号创造词法作用域

fn foo(s: String) -> String { // ----
    let w = " world".to_string(); // |  function scope
    s + &w                             // |
} // --------------------------------
fn main() {
    let s = "hello".to_string();
    let ss = foo(s);
 // println!("{:?}", s) // Error:  use of moved value: `s`
}

Base usage: 闭包

fn main() {
    let s = "hello".to_string();
    let join = |i: &str| {s + i}; // moved s into closure scope
    assert_eq!("hello world", join(" world"));
    // println!("{:?}", s); // error[E0382]: use of moved value: `s`
}