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Std Library Types in Rust - The Rust Programming Language
Std Library Types - Rust By Example
The std library provides many custom types which expands drastically on the primitives. Some of these include:
- growable
Strings like:"hello world" - growable vectors:
[1, 2, 3] - optional types:
Option<i32> - error handling types:
Result<i32, i32> - heap allocated pointers:
Box<i32>
Box, stack and heap
All values in Rust are stack allocated by default. Values can be boxed (allocated on the heap) by creating a Box<T>. A box is a smart pointer to a heap allocated value of type T. When a box goes out of scope, its destructor is called, the inner object is destroyed, and the memory on the heap is freed.
Boxed values can be dereferenced using the * operator; this removes one layer of indirection.
use std::mem;
#[allow(dead_code)]
#[derive(Debug, Clone, Copy)]
struct Point {
x: f64,
y: f64,
}
// A Rectangle can be specified by where its top left and bottom right
// corners are in space
#[allow(dead_code)]
struct Rectangle {
top_left: Point,
bottom_right: Point,
}
fn origin() -> Point {
Point { x: 0.0, y: 0.0 }
}
fn boxed_origin() -> Box<Point> {
// Allocate this point on the heap, and return a pointer to it
Box::new(Point { x: 0.0, y: 0.0 })
}
fn main() {
// (all the type annotations are superfluous)
// Stack allocated variables
let point: Point = origin();
let rectangle: Rectangle = Rectangle {
top_left: origin(),
bottom_right: Point { x: 3.0, y: -4.0 }
};
// Heap allocated rectangle
let boxed_rectangle: Box<Rectangle> = Box::new(Rectangle {
top_left: origin(),
bottom_right: Point { x: 3.0, y: -4.0 },
});
// The output of functions can be boxed
let boxed_point: Box<Point> = Box::new(origin());
// Double indirection
let box_in_a_box: Box<Box<Point>> = Box::new(boxed_origin());
println!("Point occupies {} bytes on the stack",
mem::size_of_val(&point));
println!("Rectangle occupies {} bytes on the stack",
mem::size_of_val(&rectangle));
// box size == pointer size
println!("Boxed point occupies {} bytes on the stack",
mem::size_of_val(&boxed_point));
println!("Boxed rectangle occupies {} bytes on the stack",
mem::size_of_val(&boxed_rectangle));
println!("Boxed box occupies {} bytes on the stack",
mem::size_of_val(&box_in_a_box));
// Copy the data contained in `boxed_point` into `unboxed_point`
let unboxed_point: Point = *boxed_point;
println!("Unboxed point occupies {} bytes on the stack",
mem::size_of_val(&unboxed_point));
}
Vectors
Vectors are re-sizable arrays. Like slices, their size is not known at compile time, but they can grow or shrink at any time. A vector is represented using 3 parameters:
- pointer to the data
- length
- capacity
The capacity indicates how much memory is reserved for the vector. The vector can grow as long as the length is smaller than the capacity. When this threshold needs to be surpassed, the vector is reallocated with a larger capacity.
fn main() {
// Iterators can be collected into vectors
let collected_iterator: Vec<i32> = (0..10).collect();
println!("Collected (0..10) into: {:?}", collected_iterator);
// The `vec!` macro can be used to initialize a vector
let mut xs = vec![1i32, 2, 3];
println!("Initial vector: {:?}", xs);
// Insert new element at the end of the vector
println!("Push 4 into the vector");
xs.push(4);
println!("Vector: {:?}", xs);
// Error! Immutable vectors can't grow
collected_iterator.push(0);
// FIXME ^ Comment out this line
// The `len` method yields the number of elements currently stored in a vector
println!("Vector length: {}", xs.len());
// Indexing is done using the square brackets (indexing starts at 0)
println!("Second element: {}", xs[1]);
// `pop` removes the last element from the vector and returns it
println!("Pop last element: {:?}", xs.pop());
// Out of bounds indexing yields a panic
println!("Fourth element: {}", xs[3]);
// FIXME ^ Comment out this line
// `Vector`s can be easily iterated over
println!("Contents of xs:");
for x in xs.iter() {
println!("> {}", x);
}
// A `Vector` can also be iterated over while the iteration
// count is enumerated in a separate variable (`i`)
for (i, x) in xs.iter().enumerate() {
println!("In position {} we have value {}", i, x);
}
// Thanks to `iter_mut`, mutable `Vector`s can also be iterated
// over in a way that allows modifying each value
for x in xs.iter_mut() {
*x *= 3;
}
println!("Updated vector: {:?}", xs);
}
More Vec methods can be found under the std::vec module
Strings
There are two types of strings in Rust: String and &str.
A String is stored as a vector of bytes (Vec<u8>), but guaranteed to always be a valid UTF-8 sequence. String is heap allocated, growable and not null terminated.
&str is a slice (&[u8]) that always points to a valid UTF-8 sequence, and can be used to view into a String, just like &[T] is a view into Vec<T>.
fn main() {
// (all the type annotations are superfluous)
// A reference to a string allocated in read only memory
let pangram: &'static str = "the quick brown fox jumps over the lazy dog";
println!("Pangram: {}", pangram);
// Iterate over words in reverse, no new string is allocated
println!("Words in reverse");
for word in pangram.split_whitespace().rev() {
println!("> {}", word);
}
// Copy chars into a vector, sort and remove duplicates
let mut chars: Vec<char> = pangram.chars().collect();
chars.sort();
chars.dedup();
// Create an empty and growable `String`
let mut string = String::new();
for c in chars {
// Insert a char at the end of string
string.push(c);
// Insert a string at the end of string
string.push_str(", ");
}
// The trimmed string is a slice to the original string, hence no new
// allocation is performed
let chars_to_trim: &[char] = &[' ', ','];
let trimmed_str: &str = string.trim_matches(chars_to_trim);
println!("Used characters: {}", trimmed_str);
// Heap allocate a string
let alice = String::from("I like dogs");
// Allocate new memory and store the modified string there
let bob: String = alice.replace("dog", "cat");
println!("Alice says: {}", alice);
println!("Bob says: {}", bob);
}
More str/String methods can be found under the std::str and std::string modules
Literals and escapes
There are multiple ways to write string literals with special characters in them. All result in a similar &str so it's best to use the form that is the most convenient to write. Similarly there are multiple ways to write byte string literals, which all result in &[u8; N].
Generally special characters are escaped with a backslash character: \. This way you can add any character to your string, even unprintable ones and ones that you don't know how to type. If you want a literal backslash, escape it with another one: \\
String or character literal delimiters occuring within a literal must be escaped: "\"", '\''.
fn main() {
// You can use escapes to write bytes by their hexadecimal values...
let byte_escape = "I'm writing \x52\x75\x73\x74!";
println!("What are you doing\x3F (\\x3F means ?) {}", byte_escape);
// ...or Unicode code points.
let unicode_codepoint = "\u{211D}";
let character_name = "\"DOUBLE-STRUCK CAPITAL R\"";
println!("Unicode character {} (U+211D) is called {}",
unicode_codepoint, character_name );
let long_string = "String literals
can span multiple lines.
The linebreak and indentation here ->\
<- can be escaped too!";
println!("{}", long_string);
}
Sometimes there are just too many characters that need to be escaped or it's just much more convenient to write a string out as-is. This is where raw string literals come into play.
fn main() {
let raw_str = r"Escapes don't work here: \x3F \u{211D}";
println!("{}", raw_str);
// If you need quotes in a raw string, add a pair of #s
let quotes = r#"And then I said: "There is no escape!""#;
println!("{}", quotes);
// If you need "# in your string, just use more #s in the delimiter.
// There is no limit for the number of #s you can use.
let longer_delimiter = r###"A string with "# in it. And even "##!"###;
println!("{}", longer_delimiter);
}
Want a string that's not UTF-8? (Remember, str and String must be valid UTF-8). Or maybe you want an array of bytes that's mostly text? Byte strings to the rescue!
use std::str;
fn main() {
// Note that this is not actually a `&str`
let bytestring: &[u8; 21] = b"this is a byte string";
// Byte arrays don't have the `Display` trait, so printing them is a bit limited
println!("A byte string: {:?}", bytestring);
// Byte strings can have byte escapes...
let escaped = b"\x52\x75\x73\x74 as bytes";
// ...but no unicode escapes
// let escaped = b"\u{211D} is not allowed";
println!("Some escaped bytes: {:?}", escaped);
// Raw byte strings work just like raw strings
let raw_bytestring = br"\u{211D} is not escaped here";
println!("{:?}", raw_bytestring);
// Converting a byte array to `str` can fail
if let Ok(my_str) = str::from_utf8(raw_bytestring) {
println!("And the same as text: '{}'", my_str);
}
let _quotes = br#"You can also use "fancier" formatting, \
like with normal raw strings"#;
// Byte strings don't have to be UTF-8
let shift_jis = b"\x82\xe6\x82\xa8\x82\xb1\x82\xbb"; // "ようこそ" in SHIFT-JIS
// But then they can't always be converted to `str`
match str::from_utf8(shift_jis) {
Ok(my_str) => println!("Conversion successful: '{}'", my_str),
Err(e) => println!("Conversion failed: {:?}", e),
};
}
For conversions between character encodings check out the encoding crate.
A more detailed listing of the ways to write string literals and escape characters is given in the 'Tokens' chapter of the Rust Reference.
Option
Sometimes it's desirable to catch the failure of some parts of a program instead of calling panic!; this can be accomplished using the Option enum.
The Option<T> enum has two variants:
None, to indicate failure or lack of value, andSome(value), a tuple struct that wraps avaluewith typeT.
// An integer division that doesn't `panic!`
fn checked_division(dividend: i32, divisor: i32) -> Option<i32> {
if divisor == 0 {
// Failure is represented as the `None` variant
None
} else {
// Result is wrapped in a `Some` variant
Some(dividend / divisor)
}
}
// This function handles a division that may not succeed
fn try_division(dividend: i32, divisor: i32) {
// `Option` values can be pattern matched, just like other enums
match checked_division(dividend, divisor) {
None => println!("{} / {} failed!", dividend, divisor),
Some(quotient) => {
println!("{} / {} = {}", dividend, divisor, quotient)
},
}
}
fn main() {
try_division(4, 2);
try_division(1, 0);
// Binding `None` to a variable needs to be type annotated
let none: Option<i32> = None;
let _equivalent_none = None::<i32>;
let optional_float = Some(0f32);
// Unwrapping a `Some` variant will extract the value wrapped.
println!("{:?} unwraps to {:?}", optional_float, optional_float.unwrap());
// Unwrapping a `None` variant will `panic!`
println!("{:?} unwraps to {:?}", none, none.unwrap());
}
Result
We've seen that the Option enum can be used as a return value from functions that may fail, where None can be returned to indicate failure. However, sometimes it is important to express why an operation failed. To do this we have the Result enum.
The Result<T, E> enum has two variants:
Ok(value)which indicates that the operation succeeded, and wraps thevaluereturned by the operation. (valuehas typeT)Err(why), which indicates that the operation failed, and wrapswhy, which (hopefully) explains the cause of the failure. (whyhas typeE)
mod checked {
// Mathematical "errors" we want to catch
#[derive(Debug)]
pub enum MathError {
DivisionByZero,
NonPositiveLogarithm,
NegativeSquareRoot,
}
pub type MathResult = Result<f64, MathError>;
pub fn div(x: f64, y: f64) -> MathResult {
if y == 0.0 {
// This operation would `fail`, instead let's return the reason of
// the failure wrapped in `Err`
Err(MathError::DivisionByZero)
} else {
// This operation is valid, return the result wrapped in `Ok`
Ok(x / y)
}
}
pub fn sqrt(x: f64) -> MathResult {
if x < 0.0 {
Err(MathError::NegativeSquareRoot)
} else {
Ok(x.sqrt())
}
}
pub fn ln(x: f64) -> MathResult {
if x <= 0.0 {
Err(MathError::NonPositiveLogarithm)
} else {
Ok(x.ln())
}
}
}
// `op(x, y)` === `sqrt(ln(x / y))`
fn op(x: f64, y: f64) -> f64 {
// This is a three level match pyramid!
match checked::div(x, y) {
Err(why) => panic!("{:?}", why),
Ok(ratio) => match checked::ln(ratio) {
Err(why) => panic!("{:?}", why),
Ok(ln) => match checked::sqrt(ln) {
Err(why) => panic!("{:?}", why),
Ok(sqrt) => sqrt,
},
},
}
}
fn main() {
// Will this fail?
println!("{}", op(1.0, 10.0));
}
?
Chaining results using match can get pretty untidy; luckily, the ? operator can be used to make things pretty again. ? is used at the end of an expression returning a Result, and is equivalent to a match expression, where the Err(err) branch expands to an early Err(From::from(err)), and the Ok(ok) branch expands to an ok expression.
mod checked {
#[derive(Debug)]
enum MathError {
DivisionByZero,
NonPositiveLogarithm,
NegativeSquareRoot,
}
type MathResult = Result<f64, MathError>;
fn div(x: f64, y: f64) -> MathResult {
if y == 0.0 {
Err(MathError::DivisionByZero)
} else {
Ok(x / y)
}
}
fn sqrt(x: f64) -> MathResult {
if x < 0.0 {
Err(MathError::NegativeSquareRoot)
} else {
Ok(x.sqrt())
}
}
fn ln(x: f64) -> MathResult {
if x <= 0.0 {
Err(MathError::NonPositiveLogarithm)
} else {
Ok(x.ln())
}
}
// Intermediate function
fn op_(x: f64, y: f64) -> MathResult {
// if `div` "fails", then `DivisionByZero` will be `return`ed
let ratio = div(x, y)?;
// if `ln` "fails", then `NonPositiveLogarithm` will be `return`ed
let ln = ln(ratio)?;
sqrt(ln)
}
pub fn op(x: f64, y: f64) {
match op_(x, y) {
Err(why) => panic!("{}", match why {
MathError::NonPositiveLogarithm
=> "logarithm of non-positive number",
MathError::DivisionByZero
=> "division by zero",
MathError::NegativeSquareRoot
=> "square root of negative number",
}),
Ok(value) => println!("{}", value),
}
}
}
fn main() {
checked::op(1.0, 10.0);
}
Be sure to check the documentation, as there are many methods to map/compose Result.
panic!
The panic! macro can be used to generate a panic and start unwinding its stack. While unwinding, the runtime will take care of freeing all the resources owned by the thread by calling the destructor of all its objects.
Since we are dealing with programs with only one thread, panic! will cause the program to report the panic message and exit.
// Re-implementation of integer division (/)
fn division(dividend: i32, divisor: i32) -> i32 {
if divisor == 0 {
// Division by zero triggers a panic
panic!("division by zero");
} else {
dividend / divisor
}
}
// The `main` task
fn main() {
// Heap allocated integer
let _x = Box::new(0i32);
// This operation will trigger a task failure
division(3, 0);
println!("This point won't be reached!");
// `_x` should get destroyed at this point
}
Let's check that panic! doesn't leak memory.
$ rustc panic.rs && valgrind ./panic
==4401== Memcheck, a memory error detector
==4401== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==4401== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==4401== Command: ./panic
==4401==
thread '<main>' panicked at 'division by zero', panic.rs:5
==4401==
==4401== HEAP SUMMARY:
==4401== in use at exit: 0 bytes in 0 blocks
==4401== total heap usage: 18 allocs, 18 frees, 1,648 bytes allocated
==4401==
==4401== All heap blocks were freed -- no leaks are possible
==4401==
==4401== For counts of detected and suppressed errors, rerun with: -v
==4401== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
HashMap
Where vectors store values by an integer index, HashMaps store values by key. HashMap keys can be booleans, integers, strings, or any other type that implements the Eq and Hash traits. More on this in the next section.
Like vectors, HashMaps are growable, but HashMaps can also shrink themselves when they have excess space. You can create a HashMap with a certain starting capacity using HashMap::with_capacity(uint), or use HashMap::new() to get a HashMap with a default initial capacity (recommended).
use std::collections::HashMap;
fn call(number: &str) -> &str {
match number {
"798-1364" => "We're sorry, the call cannot be completed as dialed.
Please hang up and try again.",
"645-7689" => "Hello, this is Mr. Awesome's Pizza. My name is Fred.
What can I get for you today?",
_ => "Hi! Who is this again?"
}
}
fn main() {
let mut contacts = HashMap::new();
contacts.insert("Daniel", "798-1364");
contacts.insert("Ashley", "645-7689");
contacts.insert("Katie", "435-8291");
contacts.insert("Robert", "956-1745");
// Takes a reference and returns Option<&V>
match contacts.get(&"Daniel") {
Some(&number) => println!("Calling Daniel: {}", call(number)),
_ => println!("Don't have Daniel's number."),
}
// `HashMap::insert()` returns `None`
// if the inserted value is new, `Some(value)` otherwise
contacts.insert("Daniel", "164-6743");
match contacts.get(&"Ashley") {
Some(&number) => println!("Calling Ashley: {}", call(number)),
_ => println!("Don't have Ashley's number."),
}
contacts.remove(&"Ashley");
// `HashMap::iter()` returns an iterator that yields
// (&'a key, &'a value) pairs in arbitrary order.
for (contact, &number) in contacts.iter() {
println!("Calling {}: {}", contact, call(number));
}
}
For more information on how hashing and hash maps (sometimes called hash tables) work, have a look at Hash Table Wikipedia
Alternate/custom key types
Any type that implements the Eq and Hash traits can be a key in HashMap. This includes:
bool(though not very useful since there is only two possible keys)int,uint, and all variations thereofStringand&str(protip: you can have aHashMapkeyed byStringand call.get()with an&str)
Note that f32 and f64 do not implement Hash, likely because floating-point precision errors would make using them as hashmap keys horribly error-prone.
All collection classes implement Eq and Hash if their contained type also respectively implements Eq and Hash. For example, Vec<T> will implement Hash if T implements Hash.
You can easily implement Eq and Hash for a custom type with just one line: #[derive(PartialEq, Eq, Hash)]
The compiler will do the rest. If you want more control over the details, you can implement Eq and/or Hash yourself. This guide will not cover the specifics of implementing Hash.
To play around with using a struct in HashMap, let's try making a very simple user logon system:
use std::collections::HashMap;
// Eq requires that you derive PartialEq on the type.
#[derive(PartialEq, Eq, Hash)]
struct Account<'a>{
username: &'a str,
password: &'a str,
}
struct AccountInfo<'a>{
name: &'a str,
email: &'a str,
}
type Accounts<'a> = HashMap<Account<'a>, AccountInfo<'a>>;
fn try_logon<'a>(accounts: &Accounts<'a>,
username: &'a str, password: &'a str){
println!("Username: {}", username);
println!("Password: {}", password);
println!("Attempting logon...");
let logon = Account {
username,
password,
};
match accounts.get(&logon) {
Some(account_info) => {
println!("Successful logon!");
println!("Name: {}", account_info.name);
println!("Email: {}", account_info.email);
},
_ => println!("Login failed!"),
}
}
fn main(){
let mut accounts: Accounts = HashMap::new();
let account = Account {
username: "j.everyman",
password: "password123",
};
let account_info = AccountInfo {
name: "John Everyman",
email: "j.everyman@email.com",
};
accounts.insert(account, account_info);
try_logon(&accounts, "j.everyman", "psasword123");
try_logon(&accounts, "j.everyman", "password123");
}
HashSet
Consider a HashSet as a HashMap where we just care about the keys ( HashSet<T> is, in actuality, just a wrapper around HashMap<T, ()>).
"What's the point of that?" you ask. "I could just store the keys in a Vec."
A HashSet's unique feature is that it is guaranteed to not have duplicate elements. That's the contract that any set collection fulfills. HashSet is just one implementation. (see also: BTreeSet)
If you insert a value that is already present in the HashSet, (i.e. the new value is equal to the existing and they both have the same hash), then the new value will replace the old.
This is great for when you never want more than one of something, or when you want to know if you've already got something.
But sets can do more than that.
Sets have 4 primary operations (all of the following calls return an iterator):
union: get all the unique elements in both sets.
difference: get all the elements that are in the first set but not the second.
intersection: get all the elements that are only in both sets.
symmetric_difference: get all the elements that are in one set or the other, but not both.
Try all of these in the following example:
use std::collections::HashSet;
fn main() {
let mut a: HashSet<i32> = vec![1i32, 2, 3].into_iter().collect();
let mut b: HashSet<i32> = vec![2i32, 3, 4].into_iter().collect();
assert!(a.insert(4));
assert!(a.contains(&4));
// `HashSet::insert()` returns false if
// there was a value already present.
assert!(b.insert(4), "Value 4 is already in set B!");
// FIXME ^ Comment out this line
b.insert(5);
// If a collection's element type implements `Debug`,
// then the collection implements `Debug`.
// It usually prints its elements in the format `[elem1, elem2, ...]`
println!("A: {:?}", a);
println!("B: {:?}", b);
// Print [1, 2, 3, 4, 5] in arbitrary order
println!("Union: {:?}", a.union(&b).collect::<Vec<&i32>>());
// This should print [1]
println!("Difference: {:?}", a.difference(&b).collect::<Vec<&i32>>());
// Print [2, 3, 4] in arbitrary order.
println!("Intersection: {:?}", a.intersection(&b).collect::<Vec<&i32>>());
// Print [1, 5]
println!("Symmetric Difference: {:?}",
a.symmetric_difference(&b).collect::<Vec<&i32>>());
}
(Examples are adapted from the documentation.)
Rc
When multiple ownership is needed, Rc(Reference Counting) can be used. Rc keeps track of the number of the references which means the number of owners of the value wrapped inside an Rc.
Reference count of an Rc increases by 1 whenever an Rc is cloned, and decreases by 1 whenever one cloned Rc is dropped out of the scope. When an Rc's reference count becomes zero, which means there are no owners remained, both the Rc and the value are all dropped.
Cloning an Rc never performs a deep copy. Cloning creates just another pointer to the wrapped value, and increments the count.
use std::rc::Rc;
fn main() {
let rc_examples = "Rc examples".to_string();
{
println!("--- rc_a is created ---");
let rc_a: Rc<String> = Rc::new(rc_examples);
println!("Reference Count of rc_a: {}", Rc::strong_count(&rc_a));
{
println!("--- rc_a is cloned to rc_b ---");
let rc_b: Rc<String> = Rc::clone(&rc_a);
println!("Reference Count of rc_b: {}", Rc::strong_count(&rc_b));
println!("Reference Count of rc_a: {}", Rc::strong_count(&rc_a));
// Two `Rc`s are equal if their inner values are equal
println!("rc_a and rc_b are equal: {}", rc_a.eq(&rc_b));
// We can use methods of a value directly
println!("Length of the value inside rc_a: {}", rc_a.len());
println!("Value of rc_b: {}", rc_b);
println!("--- rc_b is dropped out of scope ---");
}
println!("Reference Count of rc_a: {}", Rc::strong_count(&rc_a));
println!("--- rc_a is dropped out of scope ---");
}
// Error! `rc_examples` already moved into `rc_a`
// And when `rc_a` is dropped, `rc_examples` is dropped together
// println!("rc_examples: {}", rc_examples);
// TODO ^ Try uncommenting this line
}
Arc
When shared ownership between threads is needed, Arc(Atomic Reference Counted) can be used. This struct, via the Clone implementation can create a reference pointer for the location of a value in the memory heap while increasing the reference counter. As it shares ownership between threads, when the last reference pointer to a value is out of scope, the variable is dropped.
fn main() {
use std::sync::Arc;
use std::thread;
// This variable declaration is where its value is specified.
let apple = Arc::new("the same apple");
for _ in 0..10 {
// Here there is no value specification as it is a pointer to a reference
// in the memory heap.
let apple = Arc::clone(&apple);
thread::spawn(move || {
// As Arc was used, threads can be spawned using the value allocated
// in the Arc variable pointer's location.
println!("{:?}", apple);
});
}
}
Original article source at https://doc.rust-lang.org
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Std Library Types in Rust - The Rust Programming Language
Std Library Types - Rust By Example
The std library provides many custom types which expands drastically on the primitives. Some of these include:
- growable
Strings like:"hello world" - growable vectors:
[1, 2, 3] - optional types:
Option<i32> - error handling types:
Result<i32, i32> - heap allocated pointers:
Box<i32>
Box, stack and heap
All values in Rust are stack allocated by default. Values can be boxed (allocated on the heap) by creating a Box<T>. A box is a smart pointer to a heap allocated value of type T. When a box goes out of scope, its destructor is called, the inner object is destroyed, and the memory on the heap is freed.
Boxed values can be dereferenced using the * operator; this removes one layer of indirection.
use std::mem;
#[allow(dead_code)]
#[derive(Debug, Clone, Copy)]
struct Point {
x: f64,
y: f64,
}
// A Rectangle can be specified by where its top left and bottom right
// corners are in space
#[allow(dead_code)]
struct Rectangle {
top_left: Point,
bottom_right: Point,
}
fn origin() -> Point {
Point { x: 0.0, y: 0.0 }
}
fn boxed_origin() -> Box<Point> {
// Allocate this point on the heap, and return a pointer to it
Box::new(Point { x: 0.0, y: 0.0 })
}
fn main() {
// (all the type annotations are superfluous)
// Stack allocated variables
let point: Point = origin();
let rectangle: Rectangle = Rectangle {
top_left: origin(),
bottom_right: Point { x: 3.0, y: -4.0 }
};
// Heap allocated rectangle
let boxed_rectangle: Box<Rectangle> = Box::new(Rectangle {
top_left: origin(),
bottom_right: Point { x: 3.0, y: -4.0 },
});
// The output of functions can be boxed
let boxed_point: Box<Point> = Box::new(origin());
// Double indirection
let box_in_a_box: Box<Box<Point>> = Box::new(boxed_origin());
println!("Point occupies {} bytes on the stack",
mem::size_of_val(&point));
println!("Rectangle occupies {} bytes on the stack",
mem::size_of_val(&rectangle));
// box size == pointer size
println!("Boxed point occupies {} bytes on the stack",
mem::size_of_val(&boxed_point));
println!("Boxed rectangle occupies {} bytes on the stack",
mem::size_of_val(&boxed_rectangle));
println!("Boxed box occupies {} bytes on the stack",
mem::size_of_val(&box_in_a_box));
// Copy the data contained in `boxed_point` into `unboxed_point`
let unboxed_point: Point = *boxed_point;
println!("Unboxed point occupies {} bytes on the stack",
mem::size_of_val(&unboxed_point));
}
Vectors
Vectors are re-sizable arrays. Like slices, their size is not known at compile time, but they can grow or shrink at any time. A vector is represented using 3 parameters:
- pointer to the data
- length
- capacity
The capacity indicates how much memory is reserved for the vector. The vector can grow as long as the length is smaller than the capacity. When this threshold needs to be surpassed, the vector is reallocated with a larger capacity.
fn main() {
// Iterators can be collected into vectors
let collected_iterator: Vec<i32> = (0..10).collect();
println!("Collected (0..10) into: {:?}", collected_iterator);
// The `vec!` macro can be used to initialize a vector
let mut xs = vec![1i32, 2, 3];
println!("Initial vector: {:?}", xs);
// Insert new element at the end of the vector
println!("Push 4 into the vector");
xs.push(4);
println!("Vector: {:?}", xs);
// Error! Immutable vectors can't grow
collected_iterator.push(0);
// FIXME ^ Comment out this line
// The `len` method yields the number of elements currently stored in a vector
println!("Vector length: {}", xs.len());
// Indexing is done using the square brackets (indexing starts at 0)
println!("Second element: {}", xs[1]);
// `pop` removes the last element from the vector and returns it
println!("Pop last element: {:?}", xs.pop());
// Out of bounds indexing yields a panic
println!("Fourth element: {}", xs[3]);
// FIXME ^ Comment out this line
// `Vector`s can be easily iterated over
println!("Contents of xs:");
for x in xs.iter() {
println!("> {}", x);
}
// A `Vector` can also be iterated over while the iteration
// count is enumerated in a separate variable (`i`)
for (i, x) in xs.iter().enumerate() {
println!("In position {} we have value {}", i, x);
}
// Thanks to `iter_mut`, mutable `Vector`s can also be iterated
// over in a way that allows modifying each value
for x in xs.iter_mut() {
*x *= 3;
}
println!("Updated vector: {:?}", xs);
}
More Vec methods can be found under the std::vec module
Strings
There are two types of strings in Rust: String and &str.
A String is stored as a vector of bytes (Vec<u8>), but guaranteed to always be a valid UTF-8 sequence. String is heap allocated, growable and not null terminated.
&str is a slice (&[u8]) that always points to a valid UTF-8 sequence, and can be used to view into a String, just like &[T] is a view into Vec<T>.
fn main() {
// (all the type annotations are superfluous)
// A reference to a string allocated in read only memory
let pangram: &'static str = "the quick brown fox jumps over the lazy dog";
println!("Pangram: {}", pangram);
// Iterate over words in reverse, no new string is allocated
println!("Words in reverse");
for word in pangram.split_whitespace().rev() {
println!("> {}", word);
}
// Copy chars into a vector, sort and remove duplicates
let mut chars: Vec<char> = pangram.chars().collect();
chars.sort();
chars.dedup();
// Create an empty and growable `String`
let mut string = String::new();
for c in chars {
// Insert a char at the end of string
string.push(c);
// Insert a string at the end of string
string.push_str(", ");
}
// The trimmed string is a slice to the original string, hence no new
// allocation is performed
let chars_to_trim: &[char] = &[' ', ','];
let trimmed_str: &str = string.trim_matches(chars_to_trim);
println!("Used characters: {}", trimmed_str);
// Heap allocate a string
let alice = String::from("I like dogs");
// Allocate new memory and store the modified string there
let bob: String = alice.replace("dog", "cat");
println!("Alice says: {}", alice);
println!("Bob says: {}", bob);
}
More str/String methods can be found under the std::str and std::string modules
Literals and escapes
There are multiple ways to write string literals with special characters in them. All result in a similar &str so it's best to use the form that is the most convenient to write. Similarly there are multiple ways to write byte string literals, which all result in &[u8; N].
Generally special characters are escaped with a backslash character: \. This way you can add any character to your string, even unprintable ones and ones that you don't know how to type. If you want a literal backslash, escape it with another one: \\
String or character literal delimiters occuring within a literal must be escaped: "\"", '\''.
fn main() {
// You can use escapes to write bytes by their hexadecimal values...
let byte_escape = "I'm writing \x52\x75\x73\x74!";
println!("What are you doing\x3F (\\x3F means ?) {}", byte_escape);
// ...or Unicode code points.
let unicode_codepoint = "\u{211D}";
let character_name = "\"DOUBLE-STRUCK CAPITAL R\"";
println!("Unicode character {} (U+211D) is called {}",
unicode_codepoint, character_name );
let long_string = "String literals
can span multiple lines.
The linebreak and indentation here ->\
<- can be escaped too!";
println!("{}", long_string);
}
Sometimes there are just too many characters that need to be escaped or it's just much more convenient to write a string out as-is. This is where raw string literals come into play.
fn main() {
let raw_str = r"Escapes don't work here: \x3F \u{211D}";
println!("{}", raw_str);
// If you need quotes in a raw string, add a pair of #s
let quotes = r#"And then I said: "There is no escape!""#;
println!("{}", quotes);
// If you need "# in your string, just use more #s in the delimiter.
// There is no limit for the number of #s you can use.
let longer_delimiter = r###"A string with "# in it. And even "##!"###;
println!("{}", longer_delimiter);
}
Want a string that's not UTF-8? (Remember, str and String must be valid UTF-8). Or maybe you want an array of bytes that's mostly text? Byte strings to the rescue!
use std::str;
fn main() {
// Note that this is not actually a `&str`
let bytestring: &[u8; 21] = b"this is a byte string";
// Byte arrays don't have the `Display` trait, so printing them is a bit limited
println!("A byte string: {:?}", bytestring);
// Byte strings can have byte escapes...
let escaped = b"\x52\x75\x73\x74 as bytes";
// ...but no unicode escapes
// let escaped = b"\u{211D} is not allowed";
println!("Some escaped bytes: {:?}", escaped);
// Raw byte strings work just like raw strings
let raw_bytestring = br"\u{211D} is not escaped here";
println!("{:?}", raw_bytestring);
// Converting a byte array to `str` can fail
if let Ok(my_str) = str::from_utf8(raw_bytestring) {
println!("And the same as text: '{}'", my_str);
}
let _quotes = br#"You can also use "fancier" formatting, \
like with normal raw strings"#;
// Byte strings don't have to be UTF-8
let shift_jis = b"\x82\xe6\x82\xa8\x82\xb1\x82\xbb"; // "ようこそ" in SHIFT-JIS
// But then they can't always be converted to `str`
match str::from_utf8(shift_jis) {
Ok(my_str) => println!("Conversion successful: '{}'", my_str),
Err(e) => println!("Conversion failed: {:?}", e),
};
}
For conversions between character encodings check out the encoding crate.
A more detailed listing of the ways to write string literals and escape characters is given in the 'Tokens' chapter of the Rust Reference.
Option
Sometimes it's desirable to catch the failure of some parts of a program instead of calling panic!; this can be accomplished using the Option enum.
The Option<T> enum has two variants:
None, to indicate failure or lack of value, andSome(value), a tuple struct that wraps avaluewith typeT.
// An integer division that doesn't `panic!`
fn checked_division(dividend: i32, divisor: i32) -> Option<i32> {
if divisor == 0 {
// Failure is represented as the `None` variant
None
} else {
// Result is wrapped in a `Some` variant
Some(dividend / divisor)
}
}
// This function handles a division that may not succeed
fn try_division(dividend: i32, divisor: i32) {
// `Option` values can be pattern matched, just like other enums
match checked_division(dividend, divisor) {
None => println!("{} / {} failed!", dividend, divisor),
Some(quotient) => {
println!("{} / {} = {}", dividend, divisor, quotient)
},
}
}
fn main() {
try_division(4, 2);
try_division(1, 0);
// Binding `None` to a variable needs to be type annotated
let none: Option<i32> = None;
let _equivalent_none = None::<i32>;
let optional_float = Some(0f32);
// Unwrapping a `Some` variant will extract the value wrapped.
println!("{:?} unwraps to {:?}", optional_float, optional_float.unwrap());
// Unwrapping a `None` variant will `panic!`
println!("{:?} unwraps to {:?}", none, none.unwrap());
}
Result
We've seen that the Option enum can be used as a return value from functions that may fail, where None can be returned to indicate failure. However, sometimes it is important to express why an operation failed. To do this we have the Result enum.
The Result<T, E> enum has two variants:
Ok(value)which indicates that the operation succeeded, and wraps thevaluereturned by the operation. (valuehas typeT)Err(why), which indicates that the operation failed, and wrapswhy, which (hopefully) explains the cause of the failure. (whyhas typeE)
mod checked {
// Mathematical "errors" we want to catch
#[derive(Debug)]
pub enum MathError {
DivisionByZero,
NonPositiveLogarithm,
NegativeSquareRoot,
}
pub type MathResult = Result<f64, MathError>;
pub fn div(x: f64, y: f64) -> MathResult {
if y == 0.0 {
// This operation would `fail`, instead let's return the reason of
// the failure wrapped in `Err`
Err(MathError::DivisionByZero)
} else {
// This operation is valid, return the result wrapped in `Ok`
Ok(x / y)
}
}
pub fn sqrt(x: f64) -> MathResult {
if x < 0.0 {
Err(MathError::NegativeSquareRoot)
} else {
Ok(x.sqrt())
}
}
pub fn ln(x: f64) -> MathResult {
if x <= 0.0 {
Err(MathError::NonPositiveLogarithm)
} else {
Ok(x.ln())
}
}
}
// `op(x, y)` === `sqrt(ln(x / y))`
fn op(x: f64, y: f64) -> f64 {
// This is a three level match pyramid!
match checked::div(x, y) {
Err(why) => panic!("{:?}", why),
Ok(ratio) => match checked::ln(ratio) {
Err(why) => panic!("{:?}", why),
Ok(ln) => match checked::sqrt(ln) {
Err(why) => panic!("{:?}", why),
Ok(sqrt) => sqrt,
},
},
}
}
fn main() {
// Will this fail?
println!("{}", op(1.0, 10.0));
}
?
Chaining results using match can get pretty untidy; luckily, the ? operator can be used to make things pretty again. ? is used at the end of an expression returning a Result, and is equivalent to a match expression, where the Err(err) branch expands to an early Err(From::from(err)), and the Ok(ok) branch expands to an ok expression.
mod checked {
#[derive(Debug)]
enum MathError {
DivisionByZero,
NonPositiveLogarithm,
NegativeSquareRoot,
}
type MathResult = Result<f64, MathError>;
fn div(x: f64, y: f64) -> MathResult {
if y == 0.0 {
Err(MathError::DivisionByZero)
} else {
Ok(x / y)
}
}
fn sqrt(x: f64) -> MathResult {
if x < 0.0 {
Err(MathError::NegativeSquareRoot)
} else {
Ok(x.sqrt())
}
}
fn ln(x: f64) -> MathResult {
if x <= 0.0 {
Err(MathError::NonPositiveLogarithm)
} else {
Ok(x.ln())
}
}
// Intermediate function
fn op_(x: f64, y: f64) -> MathResult {
// if `div` "fails", then `DivisionByZero` will be `return`ed
let ratio = div(x, y)?;
// if `ln` "fails", then `NonPositiveLogarithm` will be `return`ed
let ln = ln(ratio)?;
sqrt(ln)
}
pub fn op(x: f64, y: f64) {
match op_(x, y) {
Err(why) => panic!("{}", match why {
MathError::NonPositiveLogarithm
=> "logarithm of non-positive number",
MathError::DivisionByZero
=> "division by zero",
MathError::NegativeSquareRoot
=> "square root of negative number",
}),
Ok(value) => println!("{}", value),
}
}
}
fn main() {
checked::op(1.0, 10.0);
}
Be sure to check the documentation, as there are many methods to map/compose Result.
panic!
The panic! macro can be used to generate a panic and start unwinding its stack. While unwinding, the runtime will take care of freeing all the resources owned by the thread by calling the destructor of all its objects.
Since we are dealing with programs with only one thread, panic! will cause the program to report the panic message and exit.
// Re-implementation of integer division (/)
fn division(dividend: i32, divisor: i32) -> i32 {
if divisor == 0 {
// Division by zero triggers a panic
panic!("division by zero");
} else {
dividend / divisor
}
}
// The `main` task
fn main() {
// Heap allocated integer
let _x = Box::new(0i32);
// This operation will trigger a task failure
division(3, 0);
println!("This point won't be reached!");
// `_x` should get destroyed at this point
}
Let's check that panic! doesn't leak memory.
$ rustc panic.rs && valgrind ./panic
==4401== Memcheck, a memory error detector
==4401== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==4401== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==4401== Command: ./panic
==4401==
thread '<main>' panicked at 'division by zero', panic.rs:5
==4401==
==4401== HEAP SUMMARY:
==4401== in use at exit: 0 bytes in 0 blocks
==4401== total heap usage: 18 allocs, 18 frees, 1,648 bytes allocated
==4401==
==4401== All heap blocks were freed -- no leaks are possible
==4401==
==4401== For counts of detected and suppressed errors, rerun with: -v
==4401== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
HashMap
Where vectors store values by an integer index, HashMaps store values by key. HashMap keys can be booleans, integers, strings, or any other type that implements the Eq and Hash traits. More on this in the next section.
Like vectors, HashMaps are growable, but HashMaps can also shrink themselves when they have excess space. You can create a HashMap with a certain starting capacity using HashMap::with_capacity(uint), or use HashMap::new() to get a HashMap with a default initial capacity (recommended).
use std::collections::HashMap;
fn call(number: &str) -> &str {
match number {
"798-1364" => "We're sorry, the call cannot be completed as dialed.
Please hang up and try again.",
"645-7689" => "Hello, this is Mr. Awesome's Pizza. My name is Fred.
What can I get for you today?",
_ => "Hi! Who is this again?"
}
}
fn main() {
let mut contacts = HashMap::new();
contacts.insert("Daniel", "798-1364");
contacts.insert("Ashley", "645-7689");
contacts.insert("Katie", "435-8291");
contacts.insert("Robert", "956-1745");
// Takes a reference and returns Option<&V>
match contacts.get(&"Daniel") {
Some(&number) => println!("Calling Daniel: {}", call(number)),
_ => println!("Don't have Daniel's number."),
}
// `HashMap::insert()` returns `None`
// if the inserted value is new, `Some(value)` otherwise
contacts.insert("Daniel", "164-6743");
match contacts.get(&"Ashley") {
Some(&number) => println!("Calling Ashley: {}", call(number)),
_ => println!("Don't have Ashley's number."),
}
contacts.remove(&"Ashley");
// `HashMap::iter()` returns an iterator that yields
// (&'a key, &'a value) pairs in arbitrary order.
for (contact, &number) in contacts.iter() {
println!("Calling {}: {}", contact, call(number));
}
}
For more information on how hashing and hash maps (sometimes called hash tables) work, have a look at Hash Table Wikipedia
Alternate/custom key types
Any type that implements the Eq and Hash traits can be a key in HashMap. This includes:
bool(though not very useful since there is only two possible keys)int,uint, and all variations thereofStringand&str(protip: you can have aHashMapkeyed byStringand call.get()with an&str)
Note that f32 and f64 do not implement Hash, likely because floating-point precision errors would make using them as hashmap keys horribly error-prone.
All collection classes implement Eq and Hash if their contained type also respectively implements Eq and Hash. For example, Vec<T> will implement Hash if T implements Hash.
You can easily implement Eq and Hash for a custom type with just one line: #[derive(PartialEq, Eq, Hash)]
The compiler will do the rest. If you want more control over the details, you can implement Eq and/or Hash yourself. This guide will not cover the specifics of implementing Hash.
To play around with using a struct in HashMap, let's try making a very simple user logon system:
use std::collections::HashMap;
// Eq requires that you derive PartialEq on the type.
#[derive(PartialEq, Eq, Hash)]
struct Account<'a>{
username: &'a str,
password: &'a str,
}
struct AccountInfo<'a>{
name: &'a str,
email: &'a str,
}
type Accounts<'a> = HashMap<Account<'a>, AccountInfo<'a>>;
fn try_logon<'a>(accounts: &Accounts<'a>,
username: &'a str, password: &'a str){
println!("Username: {}", username);
println!("Password: {}", password);
println!("Attempting logon...");
let logon = Account {
username,
password,
};
match accounts.get(&logon) {
Some(account_info) => {
println!("Successful logon!");
println!("Name: {}", account_info.name);
println!("Email: {}", account_info.email);
},
_ => println!("Login failed!"),
}
}
fn main(){
let mut accounts: Accounts = HashMap::new();
let account = Account {
username: "j.everyman",
password: "password123",
};
let account_info = AccountInfo {
name: "John Everyman",
email: "j.everyman@email.com",
};
accounts.insert(account, account_info);
try_logon(&accounts, "j.everyman", "psasword123");
try_logon(&accounts, "j.everyman", "password123");
}
HashSet
Consider a HashSet as a HashMap where we just care about the keys ( HashSet<T> is, in actuality, just a wrapper around HashMap<T, ()>).
"What's the point of that?" you ask. "I could just store the keys in a Vec."
A HashSet's unique feature is that it is guaranteed to not have duplicate elements. That's the contract that any set collection fulfills. HashSet is just one implementation. (see also: BTreeSet)
If you insert a value that is already present in the HashSet, (i.e. the new value is equal to the existing and they both have the same hash), then the new value will replace the old.
This is great for when you never want more than one of something, or when you want to know if you've already got something.
But sets can do more than that.
Sets have 4 primary operations (all of the following calls return an iterator):
union: get all the unique elements in both sets.
difference: get all the elements that are in the first set but not the second.
intersection: get all the elements that are only in both sets.
symmetric_difference: get all the elements that are in one set or the other, but not both.
Try all of these in the following example:
use std::collections::HashSet;
fn main() {
let mut a: HashSet<i32> = vec![1i32, 2, 3].into_iter().collect();
let mut b: HashSet<i32> = vec![2i32, 3, 4].into_iter().collect();
assert!(a.insert(4));
assert!(a.contains(&4));
// `HashSet::insert()` returns false if
// there was a value already present.
assert!(b.insert(4), "Value 4 is already in set B!");
// FIXME ^ Comment out this line
b.insert(5);
// If a collection's element type implements `Debug`,
// then the collection implements `Debug`.
// It usually prints its elements in the format `[elem1, elem2, ...]`
println!("A: {:?}", a);
println!("B: {:?}", b);
// Print [1, 2, 3, 4, 5] in arbitrary order
println!("Union: {:?}", a.union(&b).collect::<Vec<&i32>>());
// This should print [1]
println!("Difference: {:?}", a.difference(&b).collect::<Vec<&i32>>());
// Print [2, 3, 4] in arbitrary order.
println!("Intersection: {:?}", a.intersection(&b).collect::<Vec<&i32>>());
// Print [1, 5]
println!("Symmetric Difference: {:?}",
a.symmetric_difference(&b).collect::<Vec<&i32>>());
}
(Examples are adapted from the documentation.)
Rc
When multiple ownership is needed, Rc(Reference Counting) can be used. Rc keeps track of the number of the references which means the number of owners of the value wrapped inside an Rc.
Reference count of an Rc increases by 1 whenever an Rc is cloned, and decreases by 1 whenever one cloned Rc is dropped out of the scope. When an Rc's reference count becomes zero, which means there are no owners remained, both the Rc and the value are all dropped.
Cloning an Rc never performs a deep copy. Cloning creates just another pointer to the wrapped value, and increments the count.
use std::rc::Rc;
fn main() {
let rc_examples = "Rc examples".to_string();
{
println!("--- rc_a is created ---");
let rc_a: Rc<String> = Rc::new(rc_examples);
println!("Reference Count of rc_a: {}", Rc::strong_count(&rc_a));
{
println!("--- rc_a is cloned to rc_b ---");
let rc_b: Rc<String> = Rc::clone(&rc_a);
println!("Reference Count of rc_b: {}", Rc::strong_count(&rc_b));
println!("Reference Count of rc_a: {}", Rc::strong_count(&rc_a));
// Two `Rc`s are equal if their inner values are equal
println!("rc_a and rc_b are equal: {}", rc_a.eq(&rc_b));
// We can use methods of a value directly
println!("Length of the value inside rc_a: {}", rc_a.len());
println!("Value of rc_b: {}", rc_b);
println!("--- rc_b is dropped out of scope ---");
}
println!("Reference Count of rc_a: {}", Rc::strong_count(&rc_a));
println!("--- rc_a is dropped out of scope ---");
}
// Error! `rc_examples` already moved into `rc_a`
// And when `rc_a` is dropped, `rc_examples` is dropped together
// println!("rc_examples: {}", rc_examples);
// TODO ^ Try uncommenting this line
}
Arc
When shared ownership between threads is needed, Arc(Atomic Reference Counted) can be used. This struct, via the Clone implementation can create a reference pointer for the location of a value in the memory heap while increasing the reference counter. As it shares ownership between threads, when the last reference pointer to a value is out of scope, the variable is dropped.
fn main() {
use std::sync::Arc;
use std::thread;
// This variable declaration is where its value is specified.
let apple = Arc::new("the same apple");
for _ in 0..10 {
// Here there is no value specification as it is a pointer to a reference
// in the memory heap.
let apple = Arc::clone(&apple);
thread::spawn(move || {
// As Arc was used, threads can be spawned using the value allocated
// in the Arc variable pointer's location.
println!("{:?}", apple);
});
}
}
Original article source at https://doc.rust-lang.org
#rust #programming #developer
1596826740
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.
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 variables, dead code(Code that will never run), infinite loops as well as the lifetime of variables.
#security #programming #programming-languages #rust
1643176207
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:
- An overview of Serde
- Data formats supported by Serde
- Setting up
#[derive(Serialize, Deserialize)] - Examples
- API documentation
- Release notes
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
1594369800
Introduction to Structured Query Language SQL pdf
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.
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Guide to Python Programming Language
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