Rust - 01 - Getting Started

szhshp

发布于 2023-01-05 15:55:01

2770

发布于 2023-01-05 15:55:01

Hello Cargo!

Instead of saving the result of the build in the same directory as our code, Cargo stores it in the target/debug directory.

Command	Desc
cargo new	Create a project
cargo build	Build a project
cargo build --release	Build release ver
cargo run	Run a project
cargo check	build a project without producing a binary to check for errors using cargo check

Common Programming Concepts

Variables And Mutability

Shadowing & Mutable

For same variable name, the former is shadowed by the latter

fn main() {
    let x = 5;
    let x = x + 1;
    {
        let x = x * 2;
        println!("The value of x in the inner scope is: {x}");
    }
    println!("The value of x is: {x}"); // prints 6
}

Shadowed variable can change its type

fn main() {
    let spaces = "123123123";
    let spaces = spaces.len();  /* type changed */
    println!("{spaces}");
}

For reassign the variable, you must use let keyword

fn main() {
    let x = 5;
    x = x + 1;  // Error, no let keyword on reassign
}

let allows type change, let mut disallows type changes

fn main() {
    let mut spaces = "   ";
    spaces = spaces.len(); /* Error: Disallow type change for mutable */
}

Data Types

Rust is a statically typed **language, which means that it must know the types of all variables at compile time.

#![allow(unused)]
fn main() {
    /* type annotation (u32) is required */
    let guess: u32 = "42".parse().expect("Not a number!");
}

Rust has two data type subsets: scalar and compound

Scalar Types

Integer
Integer Literals
Floating-Point
Numeric
Boolean
Character
Tuple
Array

Functions

You can define function anywhere(Before/After) within the scope of the caller
Parameter type annotation is required

fn main() {
    print_labeled_measurement(5, 'h');
}

fn print_labeled_measurement(value: i32, unit_label: char) {
    println!("The measurement is: {value}{unit_label}");
}

// You can define function anywhere(Before/After) within the scope of the caller

Statements and Expressions

fn main() {
    let x = (let y = 6); // Error: Statement `let y = 6` do not have return value
}

Expressions do not include ending semicolons. If you add a semicolon to the end of an expression, you turn it into a statement, and it will then not return a value.

fn main() {
    let y = {
        let x = 3;
        x + 1     // Attention: No semicolon, means this is a expression 	
    };  // returns 4

    println!("The value of y is: {y}");
}

Function with Return Values

fn main() {
    let x = plus_one(5);

    println!("The value of x is: {x}");
}

fn plus_one(x: i32) -> i32 {
    x + 1  // Attention: no semicolon, express with return value
}

Control Flow

if Must have boolean type

fn main() {
    let number = 12;

    if number % 4 == 0 {  // only boolean type
        println!("number is divisible by 4");
    } else if number % 3 == 0 {
        println!("number is divisible by 3");
    } else {
        println!("number is not divisible by 4, 3, or 2");
    }
}

Use if in a let Statement, but the return values must in same type

fn main() {
    let condition = true;

		// Do not work because return values are not in same type
		// let number = if condition { 5 } else { "six" };
    
		let number = if condition { 5 } else { 6 };

    println!("The value of number is: {number}");
}

Traditional loop

fn main() {
    let mut counter = 0;

    let result = loop {
        /* loop in statement */
        counter += 1;

        if counter == 10 {
            break counter * 2;  /* send the break value as return value */
        }
    };

    println!("The result is {result}");
}

While Loop

fn main() {
    let mut number = 3;

    while number != 0 {
        println!("{number}!");

        number -= 1;
    }

    println!("LIFTOFF!!!");
}

for...in loop

fn main() {
    // 1..10  is a Range from 1 to 9
    // 1..=10 is a Range from 1 to 10 
    // (1..=10).rev() is a Range from 10 to 1 
    
    for number in 1..=10 {
        println!("{number}!");
    }
    println!("DONE!!!");
}

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原始发表：2022-12-22，如有侵权请联系 cloudcommunity@tencent.com 删除

rust

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