rustlings 学习随笔
序言
rustling是一个关于rust的练习题的项目.可以帮助大家通过完成一个项目的方式练习rust的语法,我认为对于补充我rust现学现卖过程中的情况很有帮助.
下边是GPT对它的介绍:
Rustling 是专为那些想要学习 Rust 编程语言的人设计的一个交互式练习集合。无论你是编程新手还是有经验的开发者，Rustling 都能提供一个友好的环境来探索 Rust 的独特功能。
特点：
- 互动性: 通过实际编写代码并即时看到结果，你可以更好地理解 Rust 的工作原理。
- 渐进式难度: 练习按照难易程度排序，从基础到高级逐步引导你深入 Rust。
- 涵盖广泛: 练习覆盖了 Rust 的主要方面，包括所有权、借用、生命周期、错误处理等。
- 社区支持: 作为一个活跃的开源项目，Rustling 拥有一个热情的支持社区，你可以在这里找到帮助或贡献自己的力量。
- 易于安装: 只需几个简单的命令，就可以在你的机器上设置好 Rustling，并开始你的学习之旅。
structs2
// structs2.rs
//
// Address all the TODOs to make the tests pass!
//
// Execute `rustlings hint structs2` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
#[derive(Debug)]
struct Order {
name: String,
year: u32,
made_by_phone: bool,
made_by_mobile: bool,
made_by_email: bool,
item_number: u32,
count: u32,
}
fn create_order_template() -> Order {
Order {
name: String::from("Bob"),
year: 2019,
made_by_phone: false,
made_by_mobile: false,
made_by_email: true,
item_number: 123,
count: 0,
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn your_order() {
let order_template = create_order_template();
// TODO: Create your own order using the update syntax and template above!
// let your_order =
let your_order = Order {
name: String::from("Hacker in Rust"),
count: 1,
..order_template
};
assert_eq!(your_order.name, "Hacker in Rust");
assert_eq!(your_order.year, order_template.year);
assert_eq!(your_order.made_by_phone, order_template.made_by_phone);
assert_eq!(your_order.made_by_mobile, order_template.made_by_mobile);
assert_eq!(your_order.made_by_email, order_template.made_by_email);
assert_eq!(your_order.item_number, order_template.item_number);
assert_eq!(your_order.count, 1);
}
}
这里注意这个,这里有一个结构体更新语法的问题:
let your_order = Order {
name: String::from("Hacker in Rust"),
count: 1,
..order_template
};
string4
主要是分辨String和&str的区别.
hashmaps3
// hashmaps3.rs
//
// A list of scores (one per line) of a soccer match is given. Each line is of
// the form : "<team_1_name>,<team_2_name>,<team_1_goals>,<team_2_goals>"
// Example: England,France,4,2 (England scored 4 goals, France 2).
//
// You have to build a scores table containing the name of the team, goals the
// team scored, and goals the team conceded. One approach to build the scores
// table is to use a Hashmap. The solution is partially written to use a
// Hashmap, complete it to pass the test.
//
// Make me pass the tests!
//
// Execute `rustlings hint hashmaps3` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
use std::collections::HashMap;
// A structure to store the goal details of a team.
struct Team {
goals_scored: u8,
goals_conceded: u8,
}
fn build_scores_table(results: String) -> HashMap<String, Team> {
// The name of the team is the key and its associated struct is the value.
let mut scores: HashMap<String, Team> = HashMap::new();
for r in results.lines() {
let v: Vec<&str> = r.split(',').collect();
let team_1_name = v[0].to_string();
let team_1_score: u8 = v[2].parse().unwrap();
let team_2_name = v[1].to_string();
let team_2_score: u8 = v[3].parse().unwrap();
// TODO: Populate the scores table with details extracted from the
// current line. Keep in mind that goals scored by team_1
// will be the number of goals conceded from team_2, and similarly
// goals scored by team_2 will be the number of goals conceded by
// team_1.
let team_1 = scores.entry(team_1_name).or_insert(Team {
goals_scored: 0,
goals_conceded: 0,
});
team_1.goals_scored += team_1_score;
team_1.goals_conceded += team_2_score;
let team_2 = scores.entry(team_2_name).or_insert(Team {
goals_scored: 0,
goals_conceded: 0,
});
team_2.goals_scored += team_2_score;
team_2.goals_conceded += team_1_score;
}
scores
}
#[cfg(test)]
mod tests {
use super::*;
fn get_results() -> String {
let results = "".to_string()
+ "England,France,4,2\n"
+ "France,Italy,3,1\n"
+ "Poland,Spain,2,0\n"
+ "Germany,England,2,1\n";
results
}
#[test]
fn build_scores() {
let scores = build_scores_table(get_results());
let mut keys: Vec<&String> = scores.keys().collect();
keys.sort();
assert_eq!(
keys,
vec!["England", "France", "Germany", "Italy", "Poland", "Spain"]
);
}
#[test]
fn validate_team_score_1() {
let scores = build_scores_table(get_results());
let team = scores.get("England").unwrap();
assert_eq!(team.goals_scored, 5);
assert_eq!(team.goals_conceded, 4);
}
#[test]
fn validate_team_score_2() {
let scores = build_scores_table(get_results());
let team = scores.get("Spain").unwrap();
assert_eq!(team.goals_scored, 0);
assert_eq!(team.goals_conceded, 2);
}
}
自动解引用
Deref 解引用 - Rust语言圣经(Rust Course)
所有权借用
#TODO
options2
// options2.rs
//
// Execute `rustlings hint options2` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
#[cfg(test)]
mod tests {
#[test]
fn simple_option() {
let target = "rustlings";
let optional_target = Some(target);
// TODO: Make this an if let statement whose value is "Some" type
if let Some(word) = optional_target {
assert_eq!(word, target);
}
}
#[test]
fn layered_option() {
let range = 10;
let mut optional_integers: Vec<Option<i8>> = vec![None];
for i in 1..(range + 1) {
optional_integers.push(Some(i));
}
let mut cursor = range;
// TODO: make this a while let statement - remember that vector.pop also
// adds another layer of Option<T>. You can stack `Option<T>`s into
// while let and if let.
while let Some(Some(integer)) = optional_integers.pop() {
assert_eq!(integer, cursor);
cursor -= 1;
}
assert_eq!(cursor, 0);
}
}
这里注意pop本身返回的就是Option<T>,而当初push进去的成员是Some(),因此导致了需要套两层Some来做模式匹配.
options3
这里存在一个所有权的问题:
// options3.rs
//
// Execute `rustlings hint options3` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
struct Point {
x: i32,
y: i32,
}
fn main() {
let y: Option<Point> = Some(Point { x: 100, y: 200 });
match y {
Some(ref p) => println!("Co-ordinates are {},{} ", p.x, p.y),
_ => panic!("no match!"),
}
y; // Fix without deleting this line.
}
必须加上ref,不然会造成y本身因为被使用因此被move了所有权,那么match结束的时候就会被释放掉,因此只传入它的ref.
errors3
<错误>(名词)的传播
返回值 Result 和? - Rust语言圣经(Rust Course)
errors4
PartialEq Trait:
PartialEq是 Rust 标准库中的一个 trait，它允许你定义类型之间的相等性比较。- 当你为一个结构体或枚举派生
PartialEq时，编译器会自动生成一个==和!=操作符的实现，这些操作符将基于结构体或枚举的所有字段进行逐个比较。 - 如果所有字段都相等，则认为这两个实例是相等的；如果有任何一个字段不相等，则认为它们不相等。
Debug Trait
Debug是另一个标准库中的 trait，它用于格式化调试输出。- 当你为一个结构体或枚举派生
Debug时，编译器会自动生成fmt::Debug的实现，这使得你可以使用{:?}或{:#?}格式说明符来打印该类型的实例。 - 这对于调试非常有用，因为它可以帮助你查看结构体或枚举实例的内容。
error5
// errors5.rs
//
// This program uses an altered version of the code from errors4.
//
// This exercise uses some concepts that we won't get to until later in the
// course, like `Box` and the `From` trait. It's not important to understand
// them in detail right now, but you can read ahead if you like. For now, think
// of the `Box<dyn ???>` type as an "I want anything that does ???" type, which,
// given Rust's usual standards for runtime safety, should strike you as
// somewhat lenient!
//
// In short, this particular use case for boxes is for when you want to own a
// value and you care only that it is a type which implements a particular
// trait. To do so, The Box is declared as of type Box<dyn Trait> where Trait is
// the trait the compiler looks for on any value used in that context. For this
// exercise, that context is the potential errors which can be returned in a
// Result.
//
// What can we use to describe both errors? In other words, is there a trait
// which both errors implement?
//
// Execute `rustlings hint errors5` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
use std::error;
use std::fmt;
use std::num::ParseIntError;
// TODO: update the return type of `main()` to make this compile.
fn main() -> Result<(), Box<dyn error::Error>> {
let pretend_user_input = "42";
let x: i64 = pretend_user_input.parse()?;
println!("output={:?}", PositiveNonzeroInteger::new(x)?);
Ok(())
}
// Don't change anything below this line.
#[derive(PartialEq, Debug)]
struct PositiveNonzeroInteger(u64);
#[derive(PartialEq, Debug)]
enum CreationError {
Negative,
Zero,
}
impl PositiveNonzeroInteger {
fn new(value: i64) -> Result<PositiveNonzeroInteger, CreationError> {
match value {
x if x < 0 => Err(CreationError::Negative),
x if x == 0 => Err(CreationError::Zero),
x => Ok(PositiveNonzeroInteger(x as u64)),
}
}
}
// This is required so that `CreationError` can implement `error::Error`.
impl fmt::Display for CreationError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let description = match *self {
CreationError::Negative => "number is negative",
CreationError::Zero => "number is zero",
};
f.write_str(description)
}
}
impl error::Error for CreationError {}
这里是用dyn error::Error代表的是一个实现了error::Error的struct,而不需要知道这个struct的名字.那么这个对象由编译器在下文中寻找.
意思就是说我不管你这个对象叫什么,只需要实现这个Trait就行了,我需要用到的是你这个struct关于这个Trait的特征.
特征对象指向实现了
Draw特征的类型的实例，也就是指向了Button或者SelectBox的实例，这种映射关系是存储在一张表中，可以在运行时通过特征对象找到具体调用的类型方法。
可以通过&引用或者Box<T>智能指针的方式来创建特征对象。
那么Box<dyn Trait>是一种创建特征对象的方式.
对于Box<T>智能指针本身,有解释,我的理解暂时是在堆上创建一个对象,可以看作包裹的内容是保存在堆上的对象的一个引用.
traits4
这里参考了:捋捋 Rust 中的 impl Trait 和 dyn Trait - 知乎 (zhihu.com)
由于输入的时候不能输入Box包裹,可以直接用impl Trait而不是Box<dyn Trait>.
但是返回值不能是impl Trait,因为不能返回不同类型,必须加一个包裹.
// traits4.rs
//
// Your task is to replace the '??' sections so the code compiles.
//
// Don't change any line other than the marked one.
//
// Execute `rustlings hint traits4` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
pub trait Licensed {
fn licensing_info(&self) -> String {
"some information".to_string()
}
}
struct SomeSoftware {}
struct OtherSoftware {}
impl Licensed for SomeSoftware {}
impl Licensed for OtherSoftware {}
// YOU MAY ONLY CHANGE THE NEXT LINE
fn compare_license_types(software: impl Licensed, software_two: impl Licensed) -> bool {
software.licensing_info() == software_two.licensing_info()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn compare_license_information() {
let some_software = SomeSoftware {};
let other_software = OtherSoftware {};
assert!(compare_license_types(some_software, other_software));
}
#[test]
fn compare_license_information_backwards() {
let some_software = SomeSoftware {};
let other_software = OtherSoftware {};
assert!(compare_license_types(other_software, some_software));
}
}
traits5
通过+选定对两个特征的要求.
// traits5.rs
//
// Your task is to replace the '??' sections so the code compiles.
//
// Don't change any line other than the marked one.
//
// Execute `rustlings hint traits5` or use the `hint` watch subcommand for a
// hint.
pub trait SomeTrait {
fn some_function(&self) -> bool {
true
}
}
pub trait OtherTrait {
fn other_function(&self) -> bool {
true
}
}
struct SomeStruct {}
struct OtherStruct {}
impl SomeTrait for SomeStruct {}
impl OtherTrait for SomeStruct {}
impl SomeTrait for OtherStruct {}
impl OtherTrait for OtherStruct {}
// YOU MAY ONLY CHANGE THE NEXT LINE
fn some_func(item: impl SomeTrait + OtherTrait) -> bool {
item.some_function() && item.other_function()
}
fn main() {
some_func(SomeStruct {});
some_func(OtherStruct {});
}
quiz3
这里考察的是可以给泛型的每个类型单独写方法.
// quiz3.rs
//
// This quiz tests:
// - Generics
// - Traits
//
// An imaginary magical school has a new report card generation system written
// in Rust! Currently the system only supports creating report cards where the
// student's grade is represented numerically (e.g. 1.0 -> 5.5). However, the
// school also issues alphabetical grades (A+ -> F-) and needs to be able to
// print both types of report card!
//
// Make the necessary code changes in the struct ReportCard and the impl block
// to support alphabetical report cards. Change the Grade in the second test to
// "A+" to show that your changes allow alphabetical grades.
//
// Execute `rustlings hint quiz3` or use the `hint` watch subcommand for a hint.
pub struct ReportCard<T> {
pub grade: T,
pub student_name: String,
pub student_age: u8,
}
impl ReportCard<f32> {
pub fn print(&self) -> String {
format!("{} ({}) - achieved a grade of {}",
&self.student_name, &self.student_age, &self.grade)
}
}
impl ReportCard<&str> {
pub fn print(&self) -> String {
format!("{} ({}) - achieved a grade of {}",
&self.student_name, &self.student_age, &self.grade)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn generate_numeric_report_card() {
let report_card = ReportCard {
grade: 2.1,
student_name: "Tom Wriggle".to_string(),
student_age: 12,
};
assert_eq!(
report_card.print(),
"Tom Wriggle (12) - achieved a grade of 2.1"
);
}
#[test]
fn generate_alphabetic_report_card() {
// TODO: Make sure to change the grade here after you finish the exercise.
let report_card = ReportCard {
grade: "A+",
student_name: "Gary Plotter".to_string(),
student_age: 11,
};
assert_eq!(
report_card.print(),
"Gary Plotter (11) - achieved a grade of A+"
);
}
}
lifetimes1
认识生命周期 - Rust语言圣经(Rust Course)
// lifetimes1.rs
//
// The Rust compiler needs to know how to check whether supplied references are
// valid, so that it can let the programmer know if a reference is at risk of
// going out of scope before it is used. Remember, references are borrows and do
// not own their own data. What if their owner goes out of scope?
//
// Execute `rustlings hint lifetimes1` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
if x.len() > y.len() {
x
} else {
y
}
}
fn main() {
let string1 = String::from("abcd");
let string2 = "xyz";
let result = longest(string1.as_str(), string2);
println!("The longest string is '{}'", result);
}
tests4
这个报错过不了啊!!!!
// tests4.rs
//
// Make sure that we're testing for the correct conditions!
//
// Execute `rustlings hint tests4` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
struct Rectangle {
width: i32,
height: i32
}
impl Rectangle {
// Only change the test functions themselves
pub fn new(width: i32, height: i32) -> Self {
if width <= 0 || height <= 0 {
panic!("Rectangle width and height cannot be negative!")
}
Rectangle {width, height}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn correct_width_and_height() {
// This test should check if the rectangle is the size that we pass into its constructor
let rect = Rectangle::new(10, 20);
assert_eq!(rect.width, 10); // check width
assert_eq!(rect.height, 20); // check height
}
#[test]
fn negative_width() {
// This test should check if program panics when we try to create rectangle with negative width
// let _rect = Rectangle::new(-10, 10);
}
#[test]
fn negative_height() {
// This test should check if program panics when we try to create rectangle with negative height
// let _rect = Rectangle::new(10, -10);
}
}
iterators1
- 如果一个迭代器没有
next那么会返回一个None - 三种获取迭代器的方法的不同:
iter()获取一个引用,因此这里做比较的时候也是和Some(&"banana")引用进行比较into_iter()则是直接把所有权交了,原来的值的所有权就给了这边这个迭代器对象了iter_mut()则是允许获取一个可变引用,这样就可以修改里边的内容
// iterators1.rs
//
// When performing operations on elements within a collection, iterators are
// essential. This module helps you get familiar with the structure of using an
// iterator and how to go through elements within an iterable collection.
//
// Make me compile by filling in the `???`s
//
// Execute `rustlings hint iterators1` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
fn main() {
let my_fav_fruits = vec!["banana", "custard apple", "avocado", "peach", "raspberry"];
let mut my_iterable_fav_fruits = my_fav_fruits.iter(); // TODO: Step 1
assert_eq!(my_iterable_fav_fruits.next(), Some(&"banana"));
assert_eq!(my_iterable_fav_fruits.next(), Some(&"custard apple")); // TODO: Step 2
assert_eq!(my_iterable_fav_fruits.next(), Some(&"avocado"));
assert_eq!(my_iterable_fav_fruits.next(), Some(&"peach")); // TODO: Step 3
assert_eq!(my_iterable_fav_fruits.next(), Some(&"raspberry"));
assert_eq!(my_iterable_fav_fruits.next(), None); // TODO: Step 4
}
iterator3
这里学到了:
map是惰性的,返回的还是一个迭代器collect是灵活的,可以通过collect::<>指定输出类型,甚至可以贴心地把Vec<Result<i32, DivisionError>>给输出成Result<Vec<i32>,DivisionError>
// iterators3.rs
//
// This is a bigger exercise than most of the others! You can do it! Here is
// your mission, should you choose to accept it:
// 1. Complete the divide function to get the first four tests to pass.
// 2. Get the remaining tests to pass by completing the result_with_list and
// list_of_results functions.
//
// Execute `rustlings hint iterators3` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
#[derive(Debug, PartialEq, Eq)]
pub enum DivisionError {
NotDivisible(NotDivisibleError),
DivideByZero,
}
#[derive(Debug, PartialEq, Eq)]
pub struct NotDivisibleError {
dividend: i32,
divisor: i32,
}
// Calculate `a` divided by `b` if `a` is evenly divisible by `b`.
// Otherwise, return a suitable error.
pub fn divide(a: i32, b: i32) -> Result<i32, DivisionError> {
if b == 0{
return Err(DivisionError::DivideByZero);
}
let r = a/b;
if r*b==a{
Ok(r)
}else{
Err(DivisionError::NotDivisible(NotDivisibleError{dividend:a,divisor:b}))
}
}
// Complete the function and return a value of the correct type so the test
// passes.
// Desired output: Ok([1, 11, 1426, 3])
fn result_with_list() -> Result<Vec<i32>,DivisionError> {
let numbers = vec![27, 297, 38502, 81];
let division_results = numbers.into_iter().map(|n| divide(n, 27));
division_results.collect::<Result<Vec<i32>, DivisionError>>()
}
// Complete the function and return a value of the correct type so the test
// passes.
// Desired output: [Ok(1), Ok(11), Ok(1426), Ok(3)]
fn list_of_results() -> Vec<Result<i32, DivisionError>> {
let numbers = vec![27, 297, 38502, 81];
let division_results = numbers.into_iter().map(|n| divide(n, 27));
division_results.collect::<Vec<Result<i32, DivisionError>>>()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_success() {
assert_eq!(divide(81, 9), Ok(9));
}
#[test]
fn test_not_divisible() {
assert_eq!(
divide(81, 6),
Err(DivisionError::NotDivisible(NotDivisibleError {
dividend: 81,
divisor: 6
}))
);
}
#[test]
fn test_divide_by_0() {
assert_eq!(divide(81, 0), Err(DivisionError::DivideByZero));
}
#[test]
fn test_divide_0_by_something() {
assert_eq!(divide(0, 81), Ok(0));
}
#[test]
fn test_result_with_list() {
assert_eq!(format!("{:?}", result_with_list()), "Ok([1, 11, 1426, 3])");
}
#[test]
fn test_list_of_results() {
assert_eq!(
format!("{:?}", list_of_results()),
"[Ok(1), Ok(11), Ok(1426), Ok(3)]"
);
}
}
iterators4
区间表达式 - Rust 参考手册 中文版 (rustwiki.org)
// iterators4.rs
//
// Execute `rustlings hint iterators4` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
pub fn factorial(num: u64) -> u64 {
// Complete this function to return the factorial of num
// Do not use:
// - return
// Try not to use:
// - imperative style loops (for, while)
// - additional variables
// For an extra challenge, don't use:
// - recursion
// Execute `rustlings hint iterators4` for hints.
(1..=num).product()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn factorial_of_0() {
assert_eq!(1, factorial(0));
}
#[test]
fn factorial_of_1() {
assert_eq!(1, factorial(1));
}
#[test]
fn factorial_of_2() {
assert_eq!(2, factorial(2));
}
#[test]
fn factorial_of_4() {
assert_eq!(24, factorial(4));
}
}
iterator5
这里存在一个认知问题,就是还是存在对:
- 引用和自动解引用和
* for的语法糖- 借用
不熟悉
// iterators5.rs
//
// Let's define a simple model to track Rustlings exercise progress. Progress
// will be modelled using a hash map. The name of the exercise is the key and
// the progress is the value. Two counting functions were created to count the
// number of exercises with a given progress. Recreate this counting
// functionality using iterators. Try not to use imperative loops (for, while).
// Only the two iterator methods (count_iterator and count_collection_iterator)
// need to be modified.
//
// Execute `rustlings hint iterators5` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
use std::collections::HashMap;
#[derive(Clone, Copy, PartialEq, Eq)]
enum Progress {
None,
Some,
Complete,
}
fn count_for(map: &HashMap<String, Progress>, value: Progress) -> usize {
let mut count = 0;
for val in map.values() {
if val == &value {
count += 1;
}
}
count
}
fn count_iterator(map: &HashMap<String, Progress>, value: Progress) -> usize {
// map is a hashmap with String keys and Progress values.
// map = { "variables1": Complete, "from_str": None, ... }
map.values().filter(|v| *v==&value).count()
}
fn count_collection_for(collection: &[HashMap<String, Progress>], value: Progress) -> usize {
let mut count = 0;
for map in collection {
for val in map.values() {
if val == &value {
count += 1;
}
}
}
count
}
fn count_collection_iterator(collection: &[HashMap<String, Progress>], value: Progress) -> usize {
// collection is a slice of hashmaps.
// collection = [{ "variables1": Complete, "from_str": None, ... },
// { "variables2": Complete, ... }, ... ]
collection.into_iter().map(|c| count_iterator(c,value)).sum()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn count_complete() {
let map = get_map();
assert_eq!(3, count_iterator(&map, Progress::Complete));
}
#[test]
fn count_some() {
let map = get_map();
assert_eq!(1, count_iterator(&map, Progress::Some));
}
#[test]
fn count_none() {
let map = get_map();
assert_eq!(2, count_iterator(&map, Progress::None));
}
#[test]
fn count_complete_equals_for() {
let map = get_map();
let progress_states = vec![Progress::Complete, Progress::Some, Progress::None];
for progress_state in progress_states {
assert_eq!(
count_for(&map, progress_state),
count_iterator(&map, progress_state)
);
}
}
#[test]
fn count_collection_complete() {
let collection = get_vec_map();
assert_eq!(
6,
count_collection_iterator(&collection, Progress::Complete)
);
}
#[test]
fn count_collection_some() {
let collection = get_vec_map();
assert_eq!(1, count_collection_iterator(&collection, Progress::Some));
}
#[test]
fn count_collection_none() {
let collection = get_vec_map();
assert_eq!(4, count_collection_iterator(&collection, Progress::None));
}
#[test]
fn count_collection_equals_for() {
let progress_states = vec![Progress::Complete, Progress::Some, Progress::None];
let collection = get_vec_map();
for progress_state in progress_states {
assert_eq!(
count_collection_for(&collection, progress_state),
count_collection_iterator(&collection, progress_state)
);
}
}
fn get_map() -> HashMap<String, Progress> {
use Progress::*;
let mut map = HashMap::new();
map.insert(String::from("variables1"), Complete);
map.insert(String::from("functions1"), Complete);
map.insert(String::from("hashmap1"), Complete);
map.insert(String::from("arc1"), Some);
map.insert(String::from("as_ref_mut"), None);
map.insert(String::from("from_str"), None);
map
}
fn get_vec_map() -> Vec<HashMap<String, Progress>> {
use Progress::*;
let map = get_map();
let mut other = HashMap::new();
other.insert(String::from("variables2"), Complete);
other.insert(String::from("functions2"), Complete);
other.insert(String::from("if1"), Complete);
other.insert(String::from("from_into"), None);
other.insert(String::from("try_from_into"), None);
vec![map, other]
}
}
cow1
这里如果像我一样很难理解高级语言,那么我们可以去看它的实现.
这里Cow实现了两个Trait,而且是在泛型的情况下为专门的类型适配了专门的特性.
这里这两个from就引起了我的思考:
&[T]和[T]之间有什么引用和引用的目标之间的自动转换.- 尤其是
println!输出多层引用的时候误导了我. - Deref 解引用使得这种误导更加严重,Rust中的 实现了
Deref的类型.
- 尤其是
Cow的from是根据类型实现的泛型.
根据这一节所学,可以看到本来就是在讨论Cow在面对引用和引用的目标时候有不同的表现,因此应该不是自动进行了解引用:
这里看源码看了半天找不到的原因是没有弄明白&[T],[T],Vec<T>,vec!的区别.
- 首先
[T]是数组Vec<T>是可变数组,是不同的. &[T]是一个数组的引用.vec!是一个宏,返回的是Vec<T>.
这里必须提到,Cow没有实现对于[T]的from,所以其中使用的是vec!返回的Vec<T>.
例子中,一会使用&[T]一会使用Vec<T>给了我非常大的误导
这里还有一个遗漏的点,数组切片.
let mut input = Cow::from(&slice[..]);这一句用的就是数组切片.
// cow1.rs
//
// This exercise explores the Cow, or Clone-On-Write type. Cow is a
// clone-on-write smart pointer. It can enclose and provide immutable access to
// borrowed data, and clone the data lazily when mutation or ownership is
// required. The type is designed to work with general borrowed data via the
// Borrow trait.
//
// This exercise is meant to show you what to expect when passing data to Cow.
// Fix the unit tests by checking for Cow::Owned(_) and Cow::Borrowed(_) at the
// TODO markers.
//
// Execute `rustlings hint cow1` or use the `hint` watch subcommand for a hint.
// I AM NOT DONE
use std::borrow::Cow;
fn abs_all<'a, 'b>(input: &'a mut Cow<'b, [i32]>) -> &'a mut Cow<'b, [i32]> {
for i in 0..input.len() {
let v = input[i];
if v < 0 {
// Clones into a vector if not already owned.
input.to_mut()[i] = -v;
}
}
input
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn reference_mutation() -> Result<(), &'static str> {
// Clone occurs because `input` needs to be mutated.
let slice = [-1, 0, 1];
let mut input = Cow::from(&slice[..]);
match abs_all(&mut input) {
Cow::Owned(_) => Ok(()),
_ => Err("Expected owned value"),
}
}
#[test]
fn reference_no_mutation() -> Result<(), &'static str> {
// No clone occurs because `input` doesn't need to be mutated.
let slice = [0, 1, 2];
let mut input = Cow::from(&slice[..]);
match abs_all(&mut input) {
Cow::Borrowed(_) => Ok(()),
_ => Err("Expected owned value"),
}
}
#[test]
fn owned_no_mutation() -> Result<(), &'static str> {
// We can also pass `slice` without `&` so Cow owns it directly. In this
// case no mutation occurs and thus also no clone, but the result is
// still owned because it was never borrowed or mutated.
let slice = vec![0, 1, 2];
let mut input = Cow::from(slice);
match abs_all(&mut input) {
Cow::Owned(_) => Ok(()),
_ => Err("Expected owned value"),
}
}
#[test]
fn owned_mutation() -> Result<(), &'static str> {
// Of course this is also the case if a mutation does occur. In this
// case the call to `to_mut()` returns a reference to the same data as
// before.
let slice = vec![-1, 0, 1];
let mut input = Cow::from(slice);
match abs_all(&mut input) {
Cow::Owned(_) => Ok(()),
_ => Err("Expected owned value"),
}
}
}