Rust ライブラリ

Rustでも標準で誰もが使うものが用意されている。ライブラリに相当するものをクレート(crate)と呼ぶことがある
基本的なstdにはプリミティブなデータ型やモジュール、マクロなどが定義されている
crates.ioにたくさんのパッケージがある

let f:f64 = 3.45;
let val = f.sqrt();

use std::f64;

fn main() {
	let f:f64 = 3.45;
	println!("{}の平方根={:?}", f, f.sqrt());
}

fn main() {
	let s = "hello, dogs";
	println!("{:?}", s.to_uppercase());
}

乱数はRngというトレイトを使うことができる

use rand::Rng;

fn main() {
	let mut r = rand::thread_rng();
	for _i in 1..6 {
		println!("{}", r.gen_range(1, 11));
	}
}

### クレートを使うプロジェクト
クレートの最新バージョンを調べる
$ cargo search rand
Updating crates.io index
rand = “0.8.5” # Random number generators and other randomness functionality.
tinyrand = “0.5.0” # Lightweight RNG specification and several ultrafast implementations in Rust.
bevy_rand = “0.1.0” # A plugin to integrate rand for ECS optimised RNG for the Bevy game engine.
random_derive = “0.0.0” # Procedurally defined macro for automatically deriving rand::Rand for structs and enums
faker_rand = “0.1.1” # Fake data generators for lorem ipsum, names, emails, and more
rand_derive2 = “0.1.21” # Generate customizable random types with the rand crate
fake-rand-test = “0.0.0” # Random number generators and other randomness functionality.
ndarray-rand = “0.14.0” # Constructors for randomized arrays. `rand` integration for `ndarray`.
rand_derive = “0.5.0” # `#[derive(Rand)]` macro (deprecated).
rand_core = “0.6.4” # Core random number generator traits and tools for implementation.
… and 1126 crates more (use –limit N to see more)

$ cargo new random3 –bin
Created binary (application) `random3` package

実数の数値計算
abs(), acos(), asin(), atan(), ceil(), copisign(), cos(), exp(), exp2(), floor(), fract(), ln(), log(), log10(), log2(), mul_add(), powf(), powi(), round(), signum(), sin(), sqrt(), tan(), trunc()

use std::f64;

fn main() {
	let f:f64 = 3.45;
	println!("{:?}", f.fract());
}

文字列の操作
find(), matches(), parse(), repeat(), to_lowercase(), to_uppercase(), trim(), trim_end(), trim_start()

乱数の生成
gen(), gen_range(), gen_bool(), gen_ratio(2, 3)

use rand::{thread_rng, Rng};

fn main() {
	let mut rng = thread_rng();

	for _ in 0..11 {
		let x: u16 = rng.gen();
		print!("{} ", x);
	}
}

use rand::{thread_rng, Rng};

fn main() {
	let mut rng = thread_rng();

	for _ in 0..11 {
		let x: u16 = rng.gen_range(0, 3);
		print!("{} ", x);
	}
}

### 日付日時
Date, DateTime, Duration

use chrono::{Utc, Local, DateTime};
use chrono::{Datelike, Timelike};

fn main() {
	let utc: DateTime<Utc> = Utc::now();
	println!("{}", utc);

	let local: DateTime<Local> = Local::now();
	println!("{}", local);

	println!("{}/{}/{}", local.year(), local.month(), local.day());
	println!("{:02}:{:02}:{:02}",
		local.hour(), local.minute(), local.second());
}

use std::thread;
use std::time::Duration;

fn main() {
	println!("3秒待ちます。");
	thread::sleep(Duration::from_secs(3));
	println!("3秒待ちました");
}