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书籍：The Rust Programming Language，官方学习资料，必看。 来源：
- 在线版本，https://doc.rust-lang.org/book/title-page.html
- 离线版本，rustup docs –book
playground
rust官网提供了一个在线编译运行rust代码的工具，即playground，可以不用下载rust到本地，直接在网页端运行rust代码，网站地址为：https://play.rust-lang.org/。 对于一些小的代码验证，特别的有用。 C++也早有类似的网站，例如cpp.sh
rust安全性解决的问题
- Memory leak
- Double free
- Data race
mut
rust非常强调默认immutable的概念，如果定义了一个mut变量，但是没有去mut它，那么编译器会提出警告，提示没有必要定义mut，如下代码所示：
fn main(){
let mut x = 10;
println!("x = {}", x);
}
编译结果：
Compiling playground v0.0.1 (/playground)
warning: variable does not need to be mutable
--> src/main.rs:2:9
|
2 | let mut x = 10;
| ----^
| |
| help: remove this `mut`
|
= note: `#[warn(unused_mut)]` on by default
warning: 1 warning emitted
Finished dev [unoptimized + debuginfo] target(s) in 0.51s
Running `target/debug/playground`
showdow
rust中的变量可以中途被“替换”，例如本来变量a是一个i32，但是可以重写a为String，这种特性叫做“shadow”。
shadow存在的意义是避免一些类型转换过程中多次命名，让代码命名看起来更简短清晰，例如“a_int”，“a_float”以及“a_str”都可以用“a”代替。
这是官方给出的说法。
Shadowing thus spares us from having to come up with different names, such as spaces_str and spaces_num; instead, we can reuse the simpler spaces name.
shadowu有一个小问题，和C++中的override一样，如果出现了拼写错误，没有shadow成功，是不会报错的，有可能导致逻辑不符合预期，增加调试时间。
不知道rust的shadow有没有类似C++的override关键字。
编译期间的溢出检查
rust编译器很强，能够在编译期间检查出是否存在类型溢出，有意思的是，这种检查是在语法检查之后进行的，如下代码所示
fn main(){
let mut x: u8 = 255;
x = x+1; // 类型溢出
println!("x={}",x);
let y = 10;
y = 11; // 一处语法错误
println!("y={}",y);
}
我们故意在类型溢出后面加入一段无关的语法错误，编译结果首先报出了语法错误，说明编译器是先检查语法错误的，并且发现错误后直接停止了编译。
Compiling playground v0.0.1 (/playground)
warning: value assigned to `y` is never read
--> src/main.rs:5:9
|
5 | let y = 10;
| ^
|
= note: `#[warn(unused_assignments)]` on by default
= help: maybe it is overwritten before being read?
error[E0384]: cannot assign twice to immutable variable `y`
--> src/main.rs:6:5
|
5 | let y = 10;
| -
| |
| first assignment to `y`
| help: make this binding mutable: `mut y`
6 | y = 11;
| ^^^^^^ cannot assign twice to immutable variable
error: aborting due to previous error; 1 warning emitted
For more information about this error, try `rustc --explain E0384`.
error: could not compile `playground`
To learn more, run the command again with --verbose.
如果我们把语法错误代码注释掉，如下所示：
fn main(){
let mut x: u8 = 255;
x = x+1;
println!("x={}",x);
// let y = 10;
// y = 11;
// println!("y={}",y);
}
那么运行结果为：
Compiling playground v0.0.1 (/playground)
Finished dev [unoptimized + debuginfo] target(s) in 0.50s
Running `target/debug/playground`
thread 'main' panicked at 'attempt to add with overflow', src/main.rs:3:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
整型字面量无法给浮点变量赋值
rust的类型检查真的是非常严格，整型的字面常量都无法给浮点变量赋值，如下代码所示：
fn main(){
let x: [f32;5] = [1,2,3,4,5];
println!("x={:?}", x);
}
编译结果：
Compiling playground v0.0.1 (/playground)
error[E0308]: mismatched types
--> src/main.rs:2:23
|
2 | let x: [f32;5] = [1,2,3,4,5];
| ^
| |
| expected `f32`, found integer
| help: use a float literal: `1.0`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0308`.
error: could not compile `playground`
To learn more, run the command again with --verbose.
ownership三个原则
- Each value in Rust has a variable that's called its owner.
- There can be only one owner at a time.
- When the owner goes out of scope, the value will be dropped.
翻译过来就是：
- 在Rust中，每一个“值”都会对应一个“拥有者”
- 同一时间只能有一个“拥有者”
- 当“拥有者”离开了可视范围，“值”就会被抛下。
1.8.13