介绍一些Rust的基本语法概念，这些概念在很多别的语言中找到类似的表示，有相同也有区分。
Variable and Mutability
- Rust中的变量默认是不可变的(immutable), Rust的安全性和易写并发的推手(nudge)之一
- 不可变变量并不等于常量(constants)
- 始终不可变，并且总是需要[annotate]
- 可以在任何范围内声明，包括全局(global)
- 只能用一个常量表达式(constant expression)赋值
const MAX_POINTS: u32 = 100_000; - Shadowing
- 和mut不同
- 同一个名字可以成为不同的类型
Data Types
- Rust是静态类型语言(statically typed)
- 当有多种可能性编译器无法直接推导(infer)出来时，要使用类型注解(type annotation)
let guess: u32 = "42".parse().expect("Not a number!"); - Scalar Types
- integers
- i/u 区分有无符号
- 有明确大小(an explicit size)
- 也可以使用isize/usize表示架构相关大小(64/32)
- 对于原始数值类型(primitive numeric types)，可以使用标准库的特定想法处理overflow, wrapping_*, checked_*, overflowing_*, saturating_*
- floating-point numbers
- f32, f64, 默认为f64
- Booleans
- bool
- true/false
- characters
- char
- single quotes
- 4bytes, represents a Unicode Scalar Value(U+0000~U+D7FF, U+E000~U+10FFFF)
- integers
- Compound Types
- tuples
- fixed length
- the types of the different value in the tuple don’t have to be the same
- optional type annotations
- use pattern matching to destructure a tuple value
- x.0/x.1/….is also available
- arrays
- also fixed length(use vector if the size needs to be growed or shrinked)
- every element must have the same type
- data allocated on the stack rather than the heap
- optional type annotation: [type; size]
- using indexing, e.g.[], to access array elements
- tuples
- Functions
- fn
- snake case
- can be defined anywhere(before or after usage)
- parameters
- subtle difference from argument
- must declare the type of each parameter
- statements optionally ending in an expression
- expressions do not include ending semicolons
- return values: most functions return the last expression implicitly
- Comments
- start with two slashes
// - documentation comments
- start with two slashes
- Control Flow
- arms
- condition: must be a bool, or we’ll get an error. No automatically conversion
ifis an expression- loop, while, for
- returning values from loops
foris the most common- Range(a type): e.g. (1..4), 1 included, 4 exclude
