边做边学Rust之原生数据类型

2. 原生数据类型

Rust提供了一些原生数据类型。包括：

有符号整形：i8，i16，i32，i64和isize（指针大小）
无符号整形：u8，u16，u32，u64和usize（指针大小）
浮点类型：f32，f64
字符类型是Unicode值，像‘a’,'α' 和 '∞' （4 字节长）
bool类型非true即否
单元类型()，同时值也为（）
数组，例如[1, 2, 3]
元组，例如(1, true)
变量可以使用注解标注类型。数字可以可以通过后缀后者默认的方式进行主机。整形默认为i32，浮点型默认为f64.

fn main() {
// Variables can be type annotated.
let logical: bool = true;

let a_float: f64 = 1.0;  // Regular annotation
let an_integer   = 5i32; // Suffix annotation

// Or a default will be used.
let default_float   = 3.0; // `f64`
let default_integer = 7;   // `i32`

let mut mutable = 12; // Mutable `i32`.

// Error! The type of a variable can't be changed
//mutable = true;
}

程序编译结果：

Compiling primitives v0.1.0 (file:///root/rust/examples/primitives)
src/main.rs:3:9: 3:16 warning: unused variable: `logical`, #[warn(unused_variables)] on by default
src/main.rs:3     let logical: bool = true;
^~~~~~~
src/main.rs:5:9: 5:16 warning: unused variable: `a_float`, #[warn(unused_variables)] on by default
src/main.rs:5     let a_float: f64 = 1.0;  // Regular annotation
^~~~~~~
src/main.rs:6:9: 6:19 warning: unused variable: `an_integer`, #[warn(unused_variables)] on by default
src/main.rs:6     let an_integer   = 5i32; // Suffix annotation
^~~~~~~~~~
src/main.rs:9:9: 9:22 warning: unused variable: `default_float`, #[warn(unused_variables)] on by default
src/main.rs:9     let default_float   = 3.0; // `f64`
^~~~~~~~~~~~~
src/main.rs:10:9: 10:24 warning: unused variable: `default_integer`, #[warn(unused_variables)] on by default
src/main.rs:10     let default_integer = 7;   // `i32`
^~~~~~~~~~~~~~~
src/main.rs:12:9: 12:20 warning: unused variable: `mutable`, #[warn(unused_variables)] on by default
src/main.rs:12     let mut mutable = 12; // Mutable `i32`.
^~~~~~~~~~~
src/main.rs:12:9: 12:20 warning: variable does not need to be mutable, #[warn(unused_mut)] on by default
src/main.rs:12     let mut mutable = 12; // Mutable `i32`.
^~~~~~~~~~~
Running `target/debug/primitives`

2.1 Literals and operators

整数1，浮点数1.2，字符‘a’，字符串“abc”，布尔型true和元类型()可以使用literals表示。

整数可以使用十六进制、八进制或者二进制表示，它们需要分别使用前缀：0x, 0o, 0b。

下划线可以插入到数字中间以增强可读性，例如1_000跟1000相同，0.000_001跟0.000001相同。

我们需要告诉编译器我们使用literals的类型。现在来说我们使用u32后缀来暗示literal是一个32位无符号整形，使用i32后缀来暗示一个32位符号整形。

操作符和他们的优先级跟C语言类似。

fn main() {
// Integer addition
println!("1 + 2 = {}", 1u32 + 2);

// Integer subtraction
println!("1 - 2 = {}", 1i32 - 2);
// TODO ^ Try changing `1i32` to `1u32` to see why the type is important

// Short-circuiting boolean logic
println!("true AND false is {}", true && false);
println!("true OR false is {}", true || false);
println!("NOT true is {}", !true);

// Bitwise operations
println!("0011 AND 0101 is {:04b}", 0b0011u32 & 0b0101);
println!("0011 OR 0101 is {:04b}", 0b0011u32 | 0b0101);
println!("0011 XOR 0101 is {:04b}", 0b0011u32 ^ 0b0101);
println!("1 << 5 is {}", 1u32 << 5);
println!("0x80 >> 2 is 0x{:x}", 0x80u32 >> 2);

// Use underscores to improve readability!
println!("One million is written as {}", 1_000_000u32);
}

程序执行结果：

1 + 2 = 3
1 - 2 = -1
true AND false is false
true OR false is true
NOT true is false
0011 AND 0101 is 0001
0011 OR 0101 is 0111
0011 XOR 0101 is 0110
1 << 5 is 32
0x80 >> 2 is 0x20
One million is written as 1000000

2.2 元组

元组是一个不同类型值的一个集合。元组使用括号( )构建，并且每个元组是一个有类型签名（T1，T2，...）的值，T1，T2是其成员的类型。函数可以使用元组或者返回元组，因为元组何以承载任意多个值。

// Tuples can be used as function arguments and as return values
fn reverse(pair: (i32, bool)) -> (bool, i32) {
// `let` can be used to bind the members of a tuple to variables
let (integer, boolean) = pair;

(boolean, integer)
}

fn main() {
// A tuple with a bunch of different types
let long_tuple = (1u8, 2u16, 3u32, 4u64,
-1i8, -2i16, -3i32, -4i64,
0.1f32, 0.2f64,
'a', true);

// Values can be extracted from the tuple using tuple indexing
println!("long tuple first value: {}", long_tuple.0);
println!("long tuple second value: {}", long_tuple.1);

// Tuples can be tuple members
let tuple_of_tuples = ((1u8, 2u16, 2u32), (4u64, -1i8), -2i16);

// Tuples are printable
println!("tuple of tuples: {:?}", tuple_of_tuples);

let pair = (1, true);
println!("pair is {:?}", pair);

println!("the reversed pair is {:?}", reverse(pair));

// To create one element tuples, the comma is required to tell them apart
// from a literal surrounded by parentheses
println!("one element tuple: {:?}", (5u32,));
println!("just an integer: {:?}", (5u32));

//tuples can be destructured to create bindings
let tuple = (1, "hello", 4.5, true);

let (a, b, c, d) = tuple;
println!("{:?}, {:?}, {:?}, {:?}", a, b, c, d);
}

程序运行结果：

long tuple first value: 1
long tuple second value: 2
tuple of tuples: ((1, 2, 2), (4, -1), -2)
pair is (1, true)
the reversed pair is (true, 1)
one element tuple: (5,)
just an integer: 5
1, "hello", 4.5, true

2.3 数组和切片

数组是相同类型T的一些对象的集合，存储在连续内存上。数组可以使用[ ]创建，并且他们的大小在编译时可以确定的，是它们类型签名的一部分[T;size]。

切片跟数组类似，但是他们的大小在编译时是未知的。相反，一个切片是一个two-word对象，第一个字指向数据的指针，第二个字是切片的长度。切片可以用来借用一个数组的某一部分，并拥有类型签名&[T]。

use std::mem;

// This function borrows a slice
fn analyze_slice(slice: &[i32]) {
println!("first element of the slice: {}", slice[0]);
println!("the slice has {} elements", slice.len());
}

fn main() {
// Fixed-size array (type signature is superfluous)
let xs: [i32; 5] = [1, 2, 3, 4, 5];

// All elements can be initialized to the same value
let ys: [i32; 500] = [0; 500];

// Indexing starts at 0
println!("first element of the array: {}", xs[0]);
println!("second element of the array: {}", xs[1]);

// `len` returns the size of the array
println!("array size: {}", xs.len());

// Arrays are stack allocated
println!("array occupies {} bytes", mem::size_of_val(&xs));

// Arrays can be automatically borrowed as slices
println!("borrow the whole array as a slice");
analyze_slice(&xs);

// Slices can point to a section of an array
println!("borrow a section of the array as a slice");
analyze_slice(&ys[1 .. 4]);

// Out of bound indexing yields a panic
println!("{}", xs[5]);
}

程序执行结果：

first element of the array: 1
second element of the array: 2
array size: 5
array occupies 20 bytes
borrow the whole array as a slice
first element of the slice: 1
the slice has 5 elements
borrow a section of the array as a slice
first element of the slice: 0
the slice has 3 elements
thread '<main>' panicked at 'index out of bounds: the len is 5 but the index is 5', <anon>:35
playpen: application terminated with error code 101