The Rust Programming Language - Understanding Loops in Rust

Rust currently provides three approaches to performing some kind of iterative activity. They are: loop, while and for. Each approach has its own set of uses.

loop

The infinite loop is the simplest form of loop available in Rust. Using the keyword loop, Rust provides a way to loop indefinitely until some terminating statement is reached. Rust’s infinite loops look like this:

loop {
    println!("Loop forever!");
}

while

Rust also has a while loop. It looks like this:


# #![allow(unused_variables)]
#fn main() {
let mut x = 5; // mut x: i32
let mut done = false; // mut done: bool

while !done {
    x += x - 3;

    println!("{}", x);

    if x % 5 == 0 {
        done = true;
    }
}
#}

while loops are the correct choice when you’re not sure how many times you need to loop.

If you need an infinite loop, you may be tempted to write this:

while true {

However, loop is far better suited to handle this case:

loop {

Rust’s control-flow analysis treats this construct differently than a while true, since we know that it will always loop. In general, the more information we can give to the compiler, the better it can do with safety and code generation, so you should always prefer loop when you plan to loop infinitely.

for

The for loop is used to loop a particular number of times. Rust’s for loops work a bit differently than in other systems languages, however. Rust’s for loop doesn’t look like this “C-style” for loop:

for (x = 0; x < 10; x++) {
    printf( "%d\n", x );
}

Instead, it looks like this:


# #![allow(unused_variables)]
#fn main() {
for x in 0..10 {
    println!("{}", x); // x: i32
}
#}

In slightly more abstract terms,

for var in expression {
    code
}

The expression is an item that can be converted into an iterator using IntoIterator. The iterator gives back a series of elements, one element per iteration of the loop. That value is then bound to the name var, which is valid for the loop body. Once the body is over, the next value is fetched from the iterator, and we loop another time. When there are no more values, the for loop is over.

In our example, 0..10 is an expression that takes a start and an end position, and gives an iterator over those values. The upper bound is exclusive, though, so our loop will print 0 through 9, not 10.

Rust does not have the “C-style” for loop on purpose. Manually controlling each element of the loop is complicated and error prone, even for experienced C developers.

Enumerate

When you need to keep track of how many times you have already looped, you can use the .enumerate() function.

On ranges:


# #![allow(unused_variables)]
#fn main() {
for (index, value) in (5..10).enumerate() {
    println!("index = {} and value = {}", index, value);
}
#}

Outputs:

index = 0 and value = 5
index = 1 and value = 6
index = 2 and value = 7
index = 3 and value = 8
index = 4 and value = 9

Don’t forget to add the parentheses around the range.

On iterators:


# #![allow(unused_variables)]
#fn main() {
let lines = "hello\nworld".lines();

for (linenumber, line) in lines.enumerate() {
    println!("{}: {}", linenumber, line);
}
#}

Outputs:

0: hello
1: world

Ending iteration early

Let’s take a look at that while loop we had earlier:


# #![allow(unused_variables)]
#fn main() {
let mut x = 5;
let mut done = false;

while !done {
    x += x - 3;

    println!("{}", x);

    if x % 5 == 0 {
        done = true;
    }
}
#}

We had to keep a dedicated mut boolean variable binding, done, to know when we should exit out of the loop. Rust has two keywords to help us with modifying iteration: break and continue.

In this case, we can write the loop in a better way with break:


# #![allow(unused_variables)]
#fn main() {
let mut x = 5;

loop {
    x += x - 3;

    println!("{}", x);

    if x % 5 == 0 { break; }
}
#}

We now loop forever with loop and use break to break out early. Issuing an explicit return statement will also serve to terminate the loop early.

continue is similar, but instead of ending the loop, it goes to the next iteration. This will only print the odd numbers:


# #![allow(unused_variables)]
#fn main() {
for x in 0..10 {
    if x % 2 == 0 { continue; }

    println!("{}", x);
}
#}

Loop labels

You may also encounter situations where you have nested loops and need to specify which one your break or continue statement is for. Like most other languages, Rust’s break or continue apply to the innermost loop. In a situation where you would like to break or continue for one of the outer loops, you can use labels to specify which loop the break or continue statement applies to.

In the example below, we continue to the next iteration of outer loop when x is even, while we continue to the next iteration of inner loop when y is even. So it will execute the println! when both x and y are odd.


# #![allow(unused_variables)]
#fn main() {
'outer: for x in 0..10 {
    'inner: for y in 0..10 {
        if x % 2 == 0 { continue 'outer; } // Continues the loop over `x`.
        if y % 2 == 0 { continue 'inner; } // Continues the loop over `y`.
        println!("x: {}, y: {}", x, y);
    }
}
#}

#Rust #Programming #WebDev #JavaScript

What is GEEK

Buddha Community

The Rust Programming Language - Understanding Loops in Rust

RUST on programming language

The title is a bit confusing to understand the context of the content. In this blog, I am going to run around and see the different aspects of programming language rust. And talk about the concepts that it introduces that are useful for various aspects of programming.

What is Rust?

Simply putting it is a statically as well as strongly typed programming language.

Let me explain:

_statically typed _indicates that all the datatypes that are expressed in the code are known at compile time and memory allocation is done properly.

Image for post

Then what is 👆 that? Let’s just say rust knows what you want to say.

But this doesn’t mean you could declare variables for a complex data type and expect rust to understand. Here comes the next point I mentioned above.

_strongly typed _indicates that the types are designed to make it harder to write syntatically incorrect code.

If you were to do even a little mistake with the syntax or definition of variables then the errors are caught at compile time. Not just the syntax errors but there are various tests build in the compiler to check for unused variablesdead code(Code that will never run), infinite loops as well as the lifetime of variables.

#security #programming #programming-languages #rust

Serde Rust: Serialization Framework for Rust

Serde

*Serde is a framework for serializing and deserializing Rust data structures efficiently and generically.*

You may be looking for:

Serde in action

Click to show Cargo.toml. Run this code in the playground.

[dependencies]

# The core APIs, including the Serialize and Deserialize traits. Always
# required when using Serde. The "derive" feature is only required when
# using #[derive(Serialize, Deserialize)] to make Serde work with structs
# and enums defined in your crate.
serde = { version = "1.0", features = ["derive"] }

# Each data format lives in its own crate; the sample code below uses JSON
# but you may be using a different one.
serde_json = "1.0"

 

use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, Debug)]
struct Point {
    x: i32,
    y: i32,
}

fn main() {
    let point = Point { x: 1, y: 2 };

    // Convert the Point to a JSON string.
    let serialized = serde_json::to_string(&point).unwrap();

    // Prints serialized = {"x":1,"y":2}
    println!("serialized = {}", serialized);

    // Convert the JSON string back to a Point.
    let deserialized: Point = serde_json::from_str(&serialized).unwrap();

    // Prints deserialized = Point { x: 1, y: 2 }
    println!("deserialized = {:?}", deserialized);
}

Getting help

Serde is one of the most widely used Rust libraries so any place that Rustaceans congregate will be able to help you out. For chat, consider trying the #rust-questions or #rust-beginners channels of the unofficial community Discord (invite: https://discord.gg/rust-lang-community), the #rust-usage or #beginners channels of the official Rust Project Discord (invite: https://discord.gg/rust-lang), or the #general stream in Zulip. For asynchronous, consider the [rust] tag on StackOverflow, the /r/rust subreddit which has a pinned weekly easy questions post, or the Rust Discourse forum. It's acceptable to file a support issue in this repo but they tend not to get as many eyes as any of the above and may get closed without a response after some time.

Download Details:
Author: serde-rs
Source Code: https://github.com/serde-rs/serde
License: View license

#rust  #rustlang 

Cayla  Erdman

Cayla Erdman

1594369800

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SQL stands for Structured Query Language. SQL is a scripting language expected to store, control, and inquiry information put away in social databases. The main manifestation of SQL showed up in 1974, when a gathering in IBM built up the principal model of a social database. The primary business social database was discharged by Relational Software later turning out to be Oracle.

Models for SQL exist. In any case, the SQL that can be utilized on every last one of the major RDBMS today is in various flavors. This is because of two reasons:

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Right now, contrasts are noted where fitting.

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The Rust Programming Language - Understanding Loops in Rust

Rust currently provides three approaches to performing some kind of iterative activity. They are: loop, while and for. Each approach has its own set of uses.

loop

The infinite loop is the simplest form of loop available in Rust. Using the keyword loop, Rust provides a way to loop indefinitely until some terminating statement is reached. Rust’s infinite loops look like this:

loop {
    println!("Loop forever!");
}

while

Rust also has a while loop. It looks like this:


# #![allow(unused_variables)]
#fn main() {
let mut x = 5; // mut x: i32
let mut done = false; // mut done: bool

while !done {
    x += x - 3;

    println!("{}", x);

    if x % 5 == 0 {
        done = true;
    }
}
#}

while loops are the correct choice when you’re not sure how many times you need to loop.

If you need an infinite loop, you may be tempted to write this:

while true {

However, loop is far better suited to handle this case:

loop {

Rust’s control-flow analysis treats this construct differently than a while true, since we know that it will always loop. In general, the more information we can give to the compiler, the better it can do with safety and code generation, so you should always prefer loop when you plan to loop infinitely.

for

The for loop is used to loop a particular number of times. Rust’s for loops work a bit differently than in other systems languages, however. Rust’s for loop doesn’t look like this “C-style” for loop:

for (x = 0; x < 10; x++) {
    printf( "%d\n", x );
}

Instead, it looks like this:


# #![allow(unused_variables)]
#fn main() {
for x in 0..10 {
    println!("{}", x); // x: i32
}
#}

In slightly more abstract terms,

for var in expression {
    code
}

The expression is an item that can be converted into an iterator using IntoIterator. The iterator gives back a series of elements, one element per iteration of the loop. That value is then bound to the name var, which is valid for the loop body. Once the body is over, the next value is fetched from the iterator, and we loop another time. When there are no more values, the for loop is over.

In our example, 0..10 is an expression that takes a start and an end position, and gives an iterator over those values. The upper bound is exclusive, though, so our loop will print 0 through 9, not 10.

Rust does not have the “C-style” for loop on purpose. Manually controlling each element of the loop is complicated and error prone, even for experienced C developers.

Enumerate

When you need to keep track of how many times you have already looped, you can use the .enumerate() function.

On ranges:


# #![allow(unused_variables)]
#fn main() {
for (index, value) in (5..10).enumerate() {
    println!("index = {} and value = {}", index, value);
}
#}

Outputs:

index = 0 and value = 5
index = 1 and value = 6
index = 2 and value = 7
index = 3 and value = 8
index = 4 and value = 9

Don’t forget to add the parentheses around the range.

On iterators:


# #![allow(unused_variables)]
#fn main() {
let lines = "hello\nworld".lines();

for (linenumber, line) in lines.enumerate() {
    println!("{}: {}", linenumber, line);
}
#}

Outputs:

0: hello
1: world

Ending iteration early

Let’s take a look at that while loop we had earlier:


# #![allow(unused_variables)]
#fn main() {
let mut x = 5;
let mut done = false;

while !done {
    x += x - 3;

    println!("{}", x);

    if x % 5 == 0 {
        done = true;
    }
}
#}

We had to keep a dedicated mut boolean variable binding, done, to know when we should exit out of the loop. Rust has two keywords to help us with modifying iteration: break and continue.

In this case, we can write the loop in a better way with break:


# #![allow(unused_variables)]
#fn main() {
let mut x = 5;

loop {
    x += x - 3;

    println!("{}", x);

    if x % 5 == 0 { break; }
}
#}

We now loop forever with loop and use break to break out early. Issuing an explicit return statement will also serve to terminate the loop early.

continue is similar, but instead of ending the loop, it goes to the next iteration. This will only print the odd numbers:


# #![allow(unused_variables)]
#fn main() {
for x in 0..10 {
    if x % 2 == 0 { continue; }

    println!("{}", x);
}
#}

Loop labels

You may also encounter situations where you have nested loops and need to specify which one your break or continue statement is for. Like most other languages, Rust’s break or continue apply to the innermost loop. In a situation where you would like to break or continue for one of the outer loops, you can use labels to specify which loop the break or continue statement applies to.

In the example below, we continue to the next iteration of outer loop when x is even, while we continue to the next iteration of inner loop when y is even. So it will execute the println! when both x and y are odd.


# #![allow(unused_variables)]
#fn main() {
'outer: for x in 0..10 {
    'inner: for y in 0..10 {
        if x % 2 == 0 { continue 'outer; } // Continues the loop over `x`.
        if y % 2 == 0 { continue 'inner; } // Continues the loop over `y`.
        println!("x: {}, y: {}", x, y);
    }
}
#}

#Rust #Programming #WebDev #JavaScript

Biju Augustian

Biju Augustian

1574340419

Guide to Python Programming Language

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