Category: Rust

### variables

fn main() {
    let x = 13;
    println!("{}", x);

    let x: f64 = 3.14159;
    println!("{}", x);

    let x;
    x = 0;
    println!("{}", x);
}

$ target/debug/hello
13
3.14159
0

variables are modifiable.
mutable: compiler allows read and write
immutable: the compiler will only allow the variable to be read from
mutable values are denoted with a mut keyword.

fn main() {
    let mut x = 42;
    println!("{}", x);
    x = 13;
    println!("{}", x);
}

booleans: bool
unsigned integers(符号なし): u8, u16, u32, u64, u128
signed integers(符号あり): i8, i16, i32, i64, i128
pointer sized integers: usize, isize
floating point: f32, f64
tuple: (value, value, …)
arrays:
slices,
str
Numeric types can be explicitly specified by appending the type to the end of the number.(13u32, 2u8)

fn main() {
    let x = 12;
    let a = 12u8;
    let b = 4.3;
    let c = 4.3f32;
    let bv = true;
    let t = (13, false);
    let sentence = "hello world";
    println!(
    	"{} {} {} {} {} {} {} {}",
    	x, a, b, c, bv, t.0, t.1, sentence
    )
}

$ target/debug/hello
12 12 4.3 4.3 true 13 false hello world

### Basic Type Conversion
as で変換する

fn main() {
    let a = 13u8;
    let b = 7u32;
    let c = a as u32 + b;
    println!("{}", c);

    let t = true;
    println!("{}", t as u8);
}

$ target/debug/hello
20
1

### constants
constant used many times efficiently.
constant must always have explicit types.
constant names are always in SCREAMING_SNAKE_CASE.

const PI: f32 = 3.14159;

fn main() {
    println!(
    	"to make an apple {} from scratch, you must first create a universe.",
    	PI
    )
}

const PI: u8 = 12; とも書く

### Arrays
an array is a fixed length collection of data.
data type for an array is [T;N] where T is the elements type and N is the fixed length.
Individual elements can be retrieved with the x operator

fn main() {
    let nums: [i32; 3] = [1, 2, 3];
    println!("{:?}", nums);
    println!("{}", nums[1]);
}

$ target/debug/hello
[1, 2, 3]
2

なるほど

$ curl –proto ‘=https’ –tlsv1.2 -sSf https://sh.rustup.rs | sh
$ sudo apt install cargo
$ cargo new –bin hello
$ cd hello
$ cargo build
Compiling hello v0.1.0 (/home/vagrant/dev/rust/hello)
Finished dev [unoptimized + debuginfo] target(s) in 0.32s
$ tree
.
├── Cargo.lock
├── Cargo.toml
├── src
│   └── main.rs
└── target
├── CACHEDIR.TAG
└── debug
├── build
├── deps
│   ├── hello-2ab4b0e0c3958f3e
│   └── hello-2ab4b0e0c3958f3e.d
├── examples
├── hello
├── hello.d
└── incremental

7 directories, 8 files

$ target/debug/hello
Hello, world!

ファイルの中身を見てみる
hello/src/main.rs

fn main() {
    println!("Hello, world!");
}

中身をtour of rustと同じにする

fn main() {
    println!("Hello, 🦀");
}

$ cargo build
$ target/debug/hello
Hello, 🦀

なるほど…