daviddoji/100-exercises-to-learn-rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Formatter (#51)

Browse Source 
Enforce consistent formatting use `dprint`
This commit is contained in:
Luca Palmieri
2024-05-24 17:00:03 +02:00
committed by GitHub
parent 537118574b
commit 99591a715e
157 changed files with 1057 additions and 1044 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
book/src/02_basic_calculator/00_intro.md
View File

@@ -1,6 +1,6 @@
# A Basic Calculator
In this chapter we'll learn how to use Rust as a **calculator**.
In this chapter we'll learn how to use Rust as a **calculator**.\
It might not sound like much, but it'll give us a chance to cover a lot of Rust's basics, such as:
- How to define and call functions

26
book/src/02_basic_calculator/01_integers.md
View File

@@ -1,6 +1,6 @@
# Types, part 1
In the ["Syntax" section](../01_intro/01_syntax.md) `compute`'s input parameters were of type `u32`.
In the ["Syntax" section](../01_intro/01_syntax.md) `compute`'s input parameters were of type `u32`.\
Let's unpack what that _means_.
## Primitive types
@@ -18,25 +18,25 @@ An integer is a number that can be written without a fractional component. E.g.
### Signed vs. unsigned
An integer can be **signed** or **unsigned**.
An integer can be **signed** or **unsigned**.\
An unsigned integer can only represent non-negative numbers (i.e. `0` or greater).
A signed integer can represent both positive and negative numbers (e.g. `-1`, `12`, etc.).
The `u` in `u32` stands for **unsigned**.
The `u` in `u32` stands for **unsigned**.\
The equivalent type for signed integer is `i32`, where the `i` stands for integer (i.e. any integer, positive or
negative).
### Bit width
The `32` in `u32` refers to the **number of bits[^bit]** used to represent the number in memory.
The `32` in `u32` refers to the **number of bits[^bit]** used to represent the number in memory.\
The more bits, the larger the range of numbers that can be represented.
Rust supports multiple bit widths for integers: `8`, `16`, `32`, `64`, `128`.
With 32 bits, `u32` can represent numbers from `0` to `2^32 - 1` (a.k.a. [`u32::MAX`](https://doc.rust-lang.org/std/primitive.u32.html#associatedconstant.MAX)).
With 32 bits, `u32` can represent numbers from `0` to `2^32 - 1` (a.k.a. [`u32::MAX`](https://doc.rust-lang.org/std/primitive.u32.html#associatedconstant.MAX)).\
With the same number of bits, a signed integer (`i32`) can represent numbers from `-2^31` to `2^31 - 1`
(i.e. from [`i32::MIN`](https://doc.rust-lang.org/std/primitive.i32.html#associatedconstant.MIN)
to [`i32::MAX`](https://doc.rust-lang.org/std/primitive.i32.html#associatedconstant.MAX)).
to [`i32::MAX`](https://doc.rust-lang.org/std/primitive.i32.html#associatedconstant.MAX)).\
The maximum value for `i32` is smaller than the maximum value for `u32` because one bit is used to represent
the sign of the number. Check out the [two's complement](https://en.wikipedia.org/wiki/Two%27s_complement)
representation for more details on how signed integers are represented in memory.
@@ -46,7 +46,7 @@ representation for more details on how signed integers are represented in memory
Combining the two variables (signed/unsigned and bit width), we get the following integer types:
| Bit width | Signed | Unsigned |
|-----------|--------|----------|
| --------- | ------ | -------- |
| 8-bit | `i8` | `u8` |
| 16-bit | `i16` | `u16` |
| 32-bit | `i32` | `u32` |
@@ -55,21 +55,21 @@ Combining the two variables (signed/unsigned and bit width), we get the followin
## Literals
A **literal** is a notation for representing a fixed value in source code.
A **literal** is a notation for representing a fixed value in source code.\
For example, `42` is a Rust literal for the number forty-two.
### Type annotations for literals
But all values in Rust have a type, so... what's the type of `42`?
The Rust compiler will try to infer the type of a literal based on how it's used.
If you don't provide any context, the compiler will default to `i32` for integer literals.
The Rust compiler will try to infer the type of a literal based on how it's used.\
If you don't provide any context, the compiler will default to `i32` for integer literals.\
If you want to use a different type, you can add the desired integer type as a suffix—e.g. `2u64` is a 2 that's
explicitly typed as a `u64`.
### Underscores in literals
You can use underscores `_` to improve the readability of large numbers.
You can use underscores `_` to improve the readability of large numbers.\
For example, `1_000_000` is the same as `1000000`.
## Arithmetic operators
@@ -82,7 +82,7 @@ Rust supports the following arithmetic operators[^traits] for integers:
- `/` for division
- `%` for remainder
Precedence and associativity rules for these operators are the same as in mathematics.
Precedence and associativity rules for these operators are the same as in mathematics.\
You can use parentheses to override the default precedence. E.g. `2 * (3 + 4)`.
> ⚠️ **Warning**
@@ -92,7 +92,7 @@ You can use parentheses to override the default precedence. E.g. `2 * (3 + 4)`.
## No automatic type coercion
As we discussed in the previous exercise, Rust is a statically typed language.
As we discussed in the previous exercise, Rust is a statically typed language.\
In particular, Rust is quite strict about type coercion. It won't automatically convert a value from one type to
another[^coercion],
even if the conversion is lossless. You have to do it explicitly.

18
book/src/02_basic_calculator/02_variables.md
View File

@@ -1,6 +1,6 @@
# Variables
In Rust, you can use the `let` keyword to declare **variables**.
In Rust, you can use the `let` keyword to declare **variables**.\
For example:
```rust
@@ -35,20 +35,20 @@ let x = 42;
let y: u32 = x;
```
In the example above, we didn't specify the type of `x`.
In the example above, we didn't specify the type of `x`.\
`x` is later assigned to `y`, which is explicitly typed as `u32`. Since Rust doesn't perform automatic type coercion,
the compiler infers the type of `x` to be `u32`—the same as `y` and the only type that will allow the program to compile
without errors.
### Inference limitations
The compiler sometimes needs a little help to infer the correct variable type based on its usage.
The compiler sometimes needs a little help to infer the correct variable type based on its usage.\
In those cases you'll get a compilation error and the compiler will ask you to provide an explicit type hint to
disambiguate the situation.
## Function arguments are variables
Not all heroes wear capes, not all variables are declared with `let`.
Not all heroes wear capes, not all variables are declared with `let`.\
Function arguments are variables too!
```rust
@@ -57,22 +57,22 @@ fn add_one(x: u32) -> u32 {
}
```
In the example above, `x` is a variable of type `u32`.
In the example above, `x` is a variable of type `u32`.\
The only difference between `x` and a variable declared with `let` is that functions arguments **must** have their type
explicitly declared. The compiler won't infer it for you.
explicitly declared. The compiler won't infer it for you.\
This constraint allows the Rust compiler (and us humans!) to understand the function's signature without having to look
at its implementation. That's a big boost for compilation speed[^speed]!
## Initialization
You don't have to initialize a variable when you declare it.
You don't have to initialize a variable when you declare it.\
For example
```rust
let x: u32;
```
is a valid variable declaration.
is a valid variable declaration.\
However, you must initialize the variable before using it. The compiler will throw an error if you don't:
```rust
@@ -101,4 +101,4 @@ help: consider assigning a value
- The exercise for this section is located in `exercises/02_basic_calculator/02_variables`
[^speed]: The Rust compiler needs all the help it can get when it comes to compilation speed.
[^speed]: The Rust compiler needs all the help it can get when it comes to compilation speed.

19
book/src/02_basic_calculator/03_if_else.md
View File

@@ -1,6 +1,6 @@
# Control flow, part 1
All our programs so far have been pretty straightforward.
All our programs so far have been pretty straightforward.\
A sequence of instructions is executed from top to bottom, and that's it.
It's time to introduce some **branching**.
@@ -23,7 +23,7 @@ This program will print `number is smaller than 5` because the condition `number
### `else` clauses
Like most programming languages, Rust supports an optional `else` branch to execute a block of code when the condition in an
`if` expression is false.
`if` expression is false.\
For example:
```rust
@@ -38,7 +38,7 @@ if number < 5 {
## Booleans
The condition in an `if` expression must be of type `bool`, a **boolean**.
The condition in an `if` expression must be of type `bool`, a **boolean**.\
Booleans, just like integers, are a primitive type in Rust.
A boolean can have one of two values: `true` or `false`.
@@ -67,12 +67,12 @@ error[E0308]: mismatched types
```
This follows from Rust's philosophy around type coercion: there's no automatic conversion from non-boolean types to booleans.
Rust doesn't have the concept of **truthy** or **falsy** values, like JavaScript or Python.
Rust doesn't have the concept of **truthy** or **falsy** values, like JavaScript or Python.\
You have to be explicit about the condition you want to check.
### Comparison operators
It's quite common to use comparison operators to build conditions for `if` expressions.
It's quite common to use comparison operators to build conditions for `if` expressions.\
Here are the comparison operators available in Rust when working with integers:
- `==`: equal to
@@ -84,7 +84,7 @@ Here are the comparison operators available in Rust when working with integers:
## `if/else` is an expression
In Rust, `if` expressions are **expressions**, not statements: they return a value.
In Rust, `if` expressions are **expressions**, not statements: they return a value.\
That value can be assigned to a variable or used in other expressions. For example:
```rust
@@ -96,11 +96,10 @@ let message = if number < 5 {
};
```
In the example above, each branch of the `if` evaluates to a string literal,
which is then assigned to the `message` variable.
In the example above, each branch of the `if` evaluates to a string literal,
which is then assigned to the `message` variable.\
The only requirement is that both `if` branches return the same type.
## References
- The exercise for this section is located in `exercises/02_basic_calculator/03_if_else`
- The exercise for this section is located in `exercises/02_basic_calculator/03_if_else`

4
book/src/02_basic_calculator/04_panics.md
View File

@@ -13,7 +13,7 @@ fn speed(start: u32, end: u32, time_elapsed: u32) -> u32 {
If you have a keen eye, you might have spotted one issue[^one]: what happens if `time_elapsed` is zero?
You can try it
out [on the Rust playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=36e5ddbe3b3f741dfa9f74c956622bac)!
out [on the Rust playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=36e5ddbe3b3f741dfa9f74c956622bac)!\
The program will exit with the following error message:
```text
@@ -21,7 +21,7 @@ thread 'main' panicked at src/main.rs:3:5:
attempt to divide by zero
```
This is known as a **panic**.
This is known as a **panic**.\
A panic is Rust's way to signal that something went so wrong that
the program can't continue executing, it's an **unrecoverable error**[^catching]. Division by zero classifies as such an
error.

2
book/src/02_basic_calculator/05_factorial.md
View File

@@ -12,4 +12,4 @@ It looks like you're ready to tackle factorials!
## References
- The exercise for this section is located in `exercises/02_basic_calculator/05_factorial`
- The exercise for this section is located in `exercises/02_basic_calculator/05_factorial`

6
book/src/02_basic_calculator/06_while.md
View File

@@ -1,6 +1,6 @@
# Loops, part 1: `while`
Your implementation of `factorial` has been forced to use recursion.
Your implementation of `factorial` has been forced to use recursion.\
This may feel natural to you, especially if you're coming from a functional programming background.
Or it may feel strange, if you're used to more imperative languages like C or Python.
@@ -8,7 +8,7 @@ Let's see how you can implement the same functionality using a **loop** instead.
## The `while` loop
A `while` loop is a way to execute a block of code as long as a **condition** is true.
A `while` loop is a way to execute a block of code as long as a **condition** is true.\
Here's the general syntax:
```rust
@@ -62,7 +62,7 @@ error[E0384]: cannot assign twice to immutable variable `i`
| ^^^^^^ cannot assign twice to immutable variable
```
This is because variables in Rust are **immutable** by default.
This is because variables in Rust are **immutable** by default.\
You can't change their value once it has been assigned.
If you want to allow modifications, you have to declare the variable as **mutable** using the `mut` keyword:

10
book/src/02_basic_calculator/07_for.md
View File

@@ -1,6 +1,6 @@
# Loops, part 2: `for`
Having to manually increment a counter variable is somewhat tedious. The pattern is also extremely common!
Having to manually increment a counter variable is somewhat tedious. The pattern is also extremely common!\
To make this easier, Rust provides a more concise way to iterate over a range of values: the `for` loop.
## The `for` loop
@@ -62,7 +62,7 @@ for i in 1..(end + 1) {
- [`for` loop documentation](https://doc.rust-lang.org/std/keyword.for.html)
[^iterator]: Later in the course we'll give a precise definition of what counts as an "iterator".
For now, think of it as a sequence of values that you can loop over.
[^weird-ranges]: You can use ranges with other types too (e.g. characters and IP addresses),
but integers are definitely the most common case in day-to-day Rust programming.
[^iterator]: Later in the course we'll give a precise definition of what counts as an "iterator".
For now, think of it as a sequence of values that you can loop over.
[^weird-ranges]: You can use ranges with other types too (e.g. characters and IP addresses),
but integers are definitely the most common case in day-to-day Rust programming.

26
book/src/02_basic_calculator/08_overflow.md
View File

@@ -1,18 +1,18 @@
# Overflow
The factorial of a number grows quite fast.
The factorial of a number grows quite fast.\
For example, the factorial of 20 is 2,432,902,008,176,640,000. That's already bigger than the maximum value for a
32-bit integer, 2,147,483,647.
When the result of an arithmetic operation is bigger than the maximum value for a given integer type,
we are talking about **an integer overflow**.
Integer overflows are an issue because they violate the contract for arithmetic operations.
Integer overflows are an issue because they violate the contract for arithmetic operations.\
The result of an arithmetic operation between two integers of a given type should be another integer of the same type.
But the _mathematically correct result_ doesn't fit into that integer type!
> If the result is smaller than the minimum value for a given integer type, we refer to the event as **an integer
> underflow**.
> underflow**.\
> For brevity, we'll only talk about integer overflows for the rest of this section, but keep in mind that
> everything we say applies to integer underflows as well.
>
@@ -32,7 +32,7 @@ is not Rust's solution to the integer overflow problem.
## Alternatives
Since we ruled out automatic promotion, what can we do when an integer overflow occurs?
Since we ruled out automatic promotion, what can we do when an integer overflow occurs?\
It boils down to two different approaches:
- Reject the operation
@@ -40,13 +40,13 @@ It boils down to two different approaches:
### Reject the operation
This is the most conservative approach: we stop the program when an integer overflow occurs.
This is the most conservative approach: we stop the program when an integer overflow occurs.\
That's done via a panic, the mechanism we've already seen in the ["Panics" section](04_panics.md).
### Come up with a "sensible" result
When the result of an arithmetic operation is bigger than the maximum value for a given integer type, you can
choose to **wrap around**.
choose to **wrap around**.\
If you think of all the possible values for a given integer type as a circle, wrapping around means that when you
reach the maximum value, you start again from the minimum value.
@@ -69,14 +69,14 @@ You may be wondering—what is a profile setting? Let's get into that!
A [**profile**](https://doc.rust-lang.org/cargo/reference/profiles.html) is a set of configuration options that can be
used to customize the way Rust code is compiled.
Cargo provides two built-in profiles: `dev` and `release`.
Cargo provides two built-in profiles: `dev` and `release`.\
The `dev` profile is used every time you run `cargo build`, `cargo run` or `cargo test`. It's aimed at local
development,
therefore it sacrifices runtime performance in favor of faster compilation times and a better debugging experience.
therefore it sacrifices runtime performance in favor of faster compilation times and a better debugging experience.\
The `release` profile, instead, is optimized for runtime performance but incurs longer compilation times. You need
to explicitly request via the `--release` flag—e.g. `cargo build --release` or `cargo run --release`.
> "Have you built your project in release mode?" is almost a meme in the Rust community.
> "Have you built your project in release mode?" is almost a meme in the Rust community.\
> It refers to developers who are not familiar with Rust and complain about its performance on
> social media (e.g. Reddit, Twitter, etc.) before realizing they haven't built their project in
> release mode.
@@ -90,12 +90,12 @@ By default, `overflow-checks` is set to:
- `true` for the `dev` profile
- `false` for the `release` profile
This is in line with the goals of the two profiles.
`dev` is aimed at local development, so it panics in order to highlight potential issues as early as possible.
This is in line with the goals of the two profiles.\
`dev` is aimed at local development, so it panics in order to highlight potential issues as early as possible.\
`release`, instead, is tuned for runtime performance: checking for overflows would slow down the program, so it
prefers to wrap around.
At the same time, having different behaviours for the two profiles can lead to subtle bugs.
At the same time, having different behaviours for the two profiles can lead to subtle bugs.\
Our recommendation is to enable `overflow-checks` for both profiles: it's better to crash than to silently produce
incorrect results. The runtime performance hit is negligible in most cases; if you're working on a performance-critical
application, you can run benchmarks to decide if it's something you can afford.
@@ -107,4 +107,4 @@ application, you can run benchmarks to decide if it's something you can afford.
## Further reading
- Check out ["Myths and legends about integer overflow in Rust"](https://huonw.github.io/blog/2016/04/myths-and-legends-about-integer-overflow-in-rust/)
for an in-depth discussion about integer overflow in Rust.
for an in-depth discussion about integer overflow in Rust.

10
book/src/02_basic_calculator/09_saturating.md
View File

@@ -1,12 +1,12 @@
# Case-by-case behavior
`overflow-checks` is a blunt tool: it's a global setting that affects the whole program.
`overflow-checks` is a blunt tool: it's a global setting that affects the whole program.\
It often happens that you want to handle integer overflows differently depending on the context: sometimes
wrapping is the right choice, other times panicking is preferable.
## `wrapping_` methods
You can opt into wrapping arithmetic on a per-operation basis by using the `wrapping_` methods[^method].
You can opt into wrapping arithmetic on a per-operation basis by using the `wrapping_` methods[^method].\
For example, you can use `wrapping_add` to add two integers with wrapping:
```rust
@@ -18,7 +18,7 @@ assert_eq!(sum, 0);
## `saturating_` methods
Alternatively, you can opt into **saturating arithmetic** by using the `saturating_` methods.
Alternatively, you can opt into **saturating arithmetic** by using the `saturating_` methods.\
Instead of wrapping around, saturating arithmetic will return the maximum or minimum value for the integer type.
For example:
@@ -29,7 +29,7 @@ let sum = x.saturating_add(y);
assert_eq!(sum, 255);
```
Since `255 + 1` is `256`, which is bigger than `u8::MAX`, the result is `u8::MAX` (255).
Since `255 + 1` is `256`, which is bigger than `u8::MAX`, the result is `u8::MAX` (255).\
The opposite happens for underflows: `0 - 1` is `-1`, which is smaller than `u8::MIN`, so the result is `u8::MIN` (0).
You can't get saturating arithmetic via the `overflow-checks` profile setting—you have to explicitly opt into it
@@ -40,4 +40,4 @@ when performing the arithmetic operation.
- The exercise for this section is located in `exercises/02_basic_calculator/09_saturating`
[^method]: You can think of methods as functions that are "attached" to a specific type.
We'll cover methods (and how to define them) in the next chapter.
We'll cover methods (and how to define them) in the next chapter.

38
book/src/02_basic_calculator/10_as_casting.md
View File

@@ -1,12 +1,12 @@
# Conversions, pt. 1
We've repeated over and over again that Rust won't perform
implicit type conversions for integers.
implicit type conversions for integers.\
How do you perform _explicit_ conversions then?
## `as`
You can use the `as` operator to convert between integer types.
You can use the `as` operator to convert between integer types.\
`as` conversions are **infallible**.
For example:
@@ -24,7 +24,7 @@ let c: u64 = a as _;
```
The semantics of this conversion are what you expect: all `u32` values are valid `u64`
values.
values.
### Truncation
@@ -38,11 +38,11 @@ let b = a as u8;
```
This program will run without issues, because `as` conversions are infallible.
But what is the value of `b`?
But what is the value of `b`?
When going from a larger integer type to a smaller, the Rust compiler will perform
a **truncation**.
a **truncation**.
To understand what happens, let's start by looking at how `256u16` is
To understand what happens, let's start by looking at how `256u16` is
represented in memory, as a sequence of bits:
```text
@@ -59,10 +59,10 @@ memory representation:
0 0 0 0 0 0 0 0
| |
+---------------+
Last 8 bits
Last 8 bits
```
Hence `256 as u8` is equal to `0`. That's... not ideal, in most scenarios.
Hence `256 as u8` is equal to `0`. That's... not ideal, in most scenarios.\
In fact, the Rust compiler will actively try to stop you if it sees you trying
to cast a literal value which will result in a truncation:
@@ -79,19 +79,19 @@ error: literal out of range for `i8`
### Recommendation
As a rule of thumb, be quite careful with `as` casting.
Use it _exclusively_ for going from a smaller type to a larger type.
To convert from a larger to smaller integer type, rely on the
[*fallible* conversion machinery](../05_ticket_v2/13_try_from.md) that we'll
As a rule of thumb, be quite careful with `as` casting.\
Use it _exclusively_ for going from a smaller type to a larger type.
To convert from a larger to smaller integer type, rely on the
[_fallible_ conversion machinery](../05_ticket_v2/13_try_from.md) that we'll
explore later in the course.
### Limitations
Surprising behaviour is not the only downside of `as` casting.
Surprising behaviour is not the only downside of `as` casting.
It is also fairly limited: you can only rely on `as` casting
for primitive types and a few other special cases.
When working with composite types, you'll have to rely on
different conversion mechanisms ([fallible](../05_ticket_v2/13_try_from.md)
for primitive types and a few other special cases.\
When working with composite types, you'll have to rely on
different conversion mechanisms ([fallible](../05_ticket_v2/13_try_from.md)
and [infallible](../04_traits/09_from.md)), which we'll explore later on.
## References
@@ -100,6 +100,6 @@ and [infallible](../04_traits/09_from.md)), which we'll explore later on.
## Further reading
- Check out [Rust's official reference](https://doc.rust-lang.org/reference/expressions/operator-expr.html#numeric-cast)
to learn the precise behaviour of `as` casting for each source/target combination,
as well as the exhaustive list of allowed conversions.
- Check out [Rust's official reference](https://doc.rust-lang.org/reference/expressions/operator-expr.html#numeric-cast)
to learn the precise behaviour of `as` casting for each source/target combination,
as well as the exhaustive list of allowed conversions.