rustlings/info.toml

# INTRO

[[exercises]]
name = "intro1"
path = "exercises/intro/intro1.rs"
mode = "compile"
hint = """
Remove the I AM NOT DONE comment in the exercises/intro/intro1.rs file
to move on to the next exercise."""

[[exercises]]
name = "intro2"
path = "exercises/intro/intro2.rs"
mode = "compile"
hint = """
Add an argument after the format string."""

# VARIABLES

[[exercises]]
name = "variables1"
path = "exercises/variables/variables1.rs"
mode = "compile"
hint = """
The declaration on line 8 is missing a keyword that is needed in Rust
to create a new variable binding."""

[[exercises]]
name = "variables2"
path = "exercises/variables/variables2.rs"
mode = "compile"
hint = """
The compiler message is saying that Rust cannot infer the type that the
variable binding `x` has with what is given here.
What happens if you annotate line 7 with a type annotation?
What if you give x a value?
What if you do both?
What type should x be, anyway?
What if x is the same type as 10? What if it's a different type?"""

[[exercises]]
name = "variables3"
path = "exercises/variables/variables3.rs"
mode = "compile"
hint = """
Oops! In this exercise, we have a variable binding that we've created on
line 7, and we're trying to use it on line 8, but we haven't given it a
value. We can't print out something that isn't there; try giving x a value!
This is an error that can cause bugs that's very easy to make in any
programming language -- thankfully the Rust compiler has caught this for us!"""

[[exercises]]
name = "variables4"
path = "exercises/variables/variables4.rs"
mode = "compile"
hint = """
In Rust, variable bindings are immutable by default. But here we're trying
to reassign a different value to x! There's a keyword we can use to make
a variable binding mutable instead."""

[[exercises]]
name = "variables5"
path = "exercises/variables/variables5.rs"
mode = "compile"
hint = """
In variables3 we already learned how to make an immutable variable mutable
using a special keyword. Unfortunately this doesn't help us much in this exercise
because we want to assign a different typed value to an existing variable. Sometimes
you may also like to reuse existing variable names because you are just converting
values to different types like in this exercise.
Fortunately Rust has a powerful solution to this problem: 'Shadowing'!
You can read more about 'Shadowing' in the book's section 'Variables and Mutability':
https://doc.rust-lang.org/book/ch03-01-variables-and-mutability.html#shadowing
Try to solve this exercise afterwards using this technique."""

[[exercises]]
name = "variables6"
path = "exercises/variables/variables6.rs"
mode = "compile"
hint = """
We know about variables and mutability, but there is another important type of
variable available: constants.
Constants are always immutable and they are declared with keyword 'const' rather
than keyword 'let'.
Constants types must also always be annotated.

Read more about constants and the differences between variables and constants under 'Constants' in the book's section 'Variables and Mutability':
https://doc.rust-lang.org/book/ch03-01-variables-and-mutability.html#constants
"""

# FUNCTIONS

[[exercises]]
name = "functions1"
path = "exercises/functions/functions1.rs"
mode = "compile"
hint = """
This main function is calling a function that it expects to exist, but the
function doesn't exist. It expects this function to have the name `call_me`.
It expects this function to not take any arguments and not return a value.
Sounds a lot like `main`, doesn't it?"""

[[exercises]]
name = "functions2"
path = "exercises/functions/functions2.rs"
mode = "compile"
hint = """
Rust requires that all parts of a function's signature have type annotations,
but `call_me` is missing the type annotation of `num`."""

[[exercises]]
name = "functions3"
path = "exercises/functions/functions3.rs"
mode = "compile"
hint = """
This time, the function *declaration* is okay, but there's something wrong
with the place where we're calling the function.
As a reminder, you can freely play around with different solutions in Rustlings!
Watch mode will only jump to the next exercise if you remove the I AM NOT DONE comment."""

[[exercises]]
name = "functions4"
path = "exercises/functions/functions4.rs"
mode = "compile"
hint = """
The error message points to line 14 and says it expects a type after the
`->`. This is where the function's return type should be-- take a look at
the `is_even` function for an example!

Also: Did you figure out that, technically, u32 would be the more fitting type
for the prices here, since they can't be negative? If so, kudos!"""

[[exercises]]
name = "functions5"
path = "exercises/functions/functions5.rs"
mode = "compile"
hint = """
This is a really common error that can be fixed by removing one character.
It happens because Rust distinguishes between expressions and statements: expressions return a value based on their operand(s), and statements simply return a () type which behaves just like `void` in C/C++ language.
We want to return a value of `i32` type from the `square` function, but it is returning a `()` type...
They are not the same. There are two solutions:
1. Add a `return` ahead of `num * num;`
2. remove `;`, make it to be `num * num`"""

# IF

[[exercises]]
name = "if1"
path = "exercises/if/if1.rs"
mode = "test"
hint = """
It's possible to do this in one line if you would like!
Some similar examples from other languages:
- In C(++) this would be: `a > b ? a : b`
- In Python this would be:  `a if a > b else b`
Remember in Rust that:
- the `if` condition does not need to be surrounded by parentheses
- `if`/`else` conditionals are expressions
- Each condition is followed by a `{}` block."""

[[exercises]]
name = "if2"
path = "exercises/if/if2.rs"
mode = "test"
hint = """
For that first compiler error, it's important in Rust that each conditional
block returns the same type! To get the tests passing, you will need a couple
conditions checking different input values."""

# QUIZ 1

[[exercises]]
name = "quiz1"
path = "exercises/quiz1.rs"
mode = "test"
hint = "No hints this time ;)"

# PRIMITIVE TYPES

[[exercises]]
name = "primitive_types1"
path = "exercises/primitive_types/primitive_types1.rs"
mode = "compile"
hint = "No hints this time ;)"

[[exercises]]
name = "primitive_types2"
path = "exercises/primitive_types/primitive_types2.rs"
mode = "compile"
hint = "No hints this time ;)"

[[exercises]]
name = "primitive_types3"
path = "exercises/primitive_types/primitive_types3.rs"
mode = "compile"
hint = """
There's a shorthand to initialize Arrays with a certain size that does not
require you to type in 100 items (but you certainly can if you want!).
For example, you can do:
let array = ["Are we there yet?"; 10];

Bonus: what are some other things you could have that would return true
for `a.len() >= 100`?"""

[[exercises]]
name = "primitive_types4"
path = "exercises/primitive_types/primitive_types4.rs"
mode = "test"
hint = """
Take a look at the Understanding Ownership -> Slices -> Other Slices section of the book:
https://doc.rust-lang.org/book/ch04-03-slices.html
and use the starting and ending indices of the items in the Array
that you want to end up in the slice.

If you're curious why the first argument of `assert_eq!` does not
have an ampersand for a reference since the second argument is a
reference, take a look at the coercion chapter of the nomicon:
https://doc.rust-lang.org/nomicon/coercions.html"""

[[exercises]]
name = "primitive_types5"
path = "exercises/primitive_types/primitive_types5.rs"
mode = "compile"
hint = """
Take a look at the Data Types -> The Tuple Type section of the book:
https://doc.rust-lang.org/book/ch03-02-data-types.html#the-tuple-type
Particularly the part about destructuring (second to last example in the section).
You'll need to make a pattern to bind `name` and `age` to the appropriate parts
of the tuple. You can do it!!"""

[[exercises]]
name = "primitive_types6"
path = "exercises/primitive_types/primitive_types6.rs"
mode = "test"
hint = """
While you could use a destructuring `let` for the tuple here, try
indexing into it instead, as explained in the last example of the
Data Types -> The Tuple Type section of the book:
https://doc.rust-lang.org/book/ch03-02-data-types.html#the-tuple-type
Now you have another tool in your toolbox!"""

# VECS

[[exercises]]
name = "vecs1"
path = "exercises/vecs/vecs1.rs"
mode = "test"
hint = """
In Rust, there are two ways to define a Vector.
1. One way is to use the `Vec::new()` function to create a new vector
  and fill it with the `push()` method.
2. The second way, which is simpler is to use the `vec![]` macro and
  define your elements inside the square brackets.
Check this chapter: https://doc.rust-lang.org/stable/book/ch08-01-vectors.html
of the Rust book to learn more.
"""

[[exercises]]
name = "vecs2"
path = "exercises/vecs/vecs2.rs"
mode = "test"
hint = """
Hint 1: `i` is each element from the Vec as they are being iterated. Can you try
multiplying this?

Hint 2: For the first function, there's a way to directly access the numbers stored
in the Vec, using the * dereference operator. You can both access and write to the
number that way.

After you've completed both functions, decide for yourself which approach you like
better. What do you think is the more commonly used pattern under Rust developers?
"""

# MOVE SEMANTICS

[[exercises]]
name = "move_semantics1"
path = "exercises/move_semantics/move_semantics1.rs"
mode = "compile"
hint = """
So you've got the "cannot borrow immutable local variable `vec1` as mutable" error on line 13,
right? The fix for this is going to be adding one keyword, and the addition is NOT on line 13
where the error is.

Also: Try accessing `vec0` after having called `fill_vec()`. See what happens!"""

[[exercises]]
name = "move_semantics2"
path = "exercises/move_semantics/move_semantics2.rs"
mode = "compile"
hint = """
So, `vec0` is passed into the `fill_vec` function as an argument. In Rust,
when an argument is passed to a function and it's not explicitly returned,
you can't use the original variable anymore. We call this "moving" a variable.
Variables that are moved into a function (or block scope) and aren't explicitly
returned get "dropped" at the end of that function. This is also what happens here.
There's a few ways to fix this, try them all if you want:
1. Make another, separate version of the data that's in `vec0` and pass that
   to `fill_vec` instead.
2. Make `fill_vec` borrow its argument instead of taking ownership of it,
   and then copy the data within the function in order to return an owned
   `Vec<i32>`
3. Make `fill_vec` *mutably* borrow a reference to its argument (which will need to be
   mutable), modify it directly, then not return anything. Then you can get rid
   of `vec1` entirely -- note that this will change what gets printed by the
   first `println!`"""

[[exercises]]
name = "move_semantics3"
path = "exercises/move_semantics/move_semantics3.rs"
mode = "compile"
hint = """
The difference between this one and the previous ones is that the first line
of `fn fill_vec` that had `let mut vec = vec;` is no longer there. You can,
instead of adding that line back, add `mut` in one place that will change
an existing binding to be a mutable binding instead of an immutable one :)"""

[[exercises]]
name = "move_semantics4"
path = "exercises/move_semantics/move_semantics4.rs"
mode = "compile"
hint = """
Stop reading whenever you feel like you have enough direction :) Or try
doing one step and then fixing the compiler errors that result!
So the end goal is to:
   - get rid of the first line in main that creates the new vector
   - so then `vec0` doesn't exist, so we can't pass it to `fill_vec`
   - we don't want to pass anything to `fill_vec`, so its signature should
     reflect that it does not take any arguments
   - since we're not creating a new vec in `main` anymore, we need to create
     a new vec in `fill_vec`, similarly to the way we did in `main`"""

[[exercises]]
name = "move_semantics5"
path = "exercises/move_semantics/move_semantics5.rs"
mode = "compile"
hint = """
Carefully reason about the range in which each mutable reference is in
scope. Does it help to update the value of referent (x) immediately after
the mutable reference is taken? Read more about 'Mutable References'
in the book's section References and Borrowing':
https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html#mutable-references.
"""

[[exercises]]
name = "move_semantics6"
path = "exercises/move_semantics/move_semantics6.rs"
mode = "compile"
hint = """
To find the answer, you can consult the book section "References and Borrowing":
https://doc.rust-lang.org/stable/book/ch04-02-references-and-borrowing.html
The first problem is that `get_char` is taking ownership of the string.
So `data` is moved and can't be used for `string_uppercase`
`data` is moved to `get_char` first, meaning that `string_uppercase` cannot manipulate the data.
Once you've fixed that, `string_uppercase`'s function signature will also need to be adjusted.
Can you figure out how?

Another hint: it has to do with the `&` character."""

# STRUCTS

[[exercises]]
name = "structs1"
path = "exercises/structs/structs1.rs"
mode = "test"
hint = """
Rust has more than one type of struct. Three actually, all variants are used to package related data together.
There are normal (or classic) structs. These are named collections of related data stored in fields.
Tuple structs are basically just named tuples.
Finally, Unit-like structs. These don't have any fields and are useful for generics.

In this exercise you need to complete and implement one of each kind.
Read more about structs in The Book: https://doc.rust-lang.org/book/ch05-01-defining-structs.html"""

[[exercises]]
name = "structs2"
path = "exercises/structs/structs2.rs"
mode = "test"
hint = """
Creating instances of structs is easy, all you need to do is assign some values to its fields.
There are however some shortcuts that can be taken when instantiating structs.
Have a look in The Book, to find out more: https://doc.rust-lang.org/stable/book/ch05-01-defining-structs.html#creating-instances-from-other-instances-with-struct-update-syntax"""

[[exercises]]
name = "structs3"
path = "exercises/structs/structs3.rs"
mode = "test"
hint = """
The new method needs to panic if the weight is physically impossible :), how do we do that in Rust?

For is_international: What makes a package international? Seems related to the places it goes through right?

For calculate_transport_fees: Bigger is more expensive usually, we don't have size, but something may fit the bill here :)

Have a look in The Book, to find out more about method implementations: https://doc.rust-lang.org/book/ch05-03-method-syntax.html"""

# ENUMS

[[exercises]]
name = "enums1"
path = "exercises/enums/enums1.rs"
mode = "compile"
hint = "No hints this time ;)"

[[exercises]]
name = "enums2"
path = "exercises/enums/enums2.rs"
mode = "compile"
hint = """
You can create enumerations that have different variants with different types
such as no data, anonymous structs, a single string, tuples, ...etc"""

[[exercises]]
name = "enums3"
path = "exercises/enums/enums3.rs"
mode = "test"
hint = """
As a first step, you can define enums to compile this code without errors.
and then create a match expression in `process()`. 
Note that you need to deconstruct some message variants 
in the match expression to get value in the variant."""

# STRINGS

[[exercises]]
name = "strings1"
path = "exercises/strings/strings1.rs"
mode = "compile"
hint = """
The `current_favorite_color` function is currently returning a string slice with the `'static`
lifetime. We know this because the data of the string lives in our code itself -- it doesn't
come from a file or user input or another program -- so it will live as long as our program
lives. But it is still a string slice. There's one way to create a `String` by converting a
string slice covered in the Strings chapter of the book, and another way that uses the `From`
trait."""

[[exercises]]
name = "strings2"
path = "exercises/strings/strings2.rs"
mode = "compile"
hint = """
Yes, it would be really easy to fix this by just changing the value bound to `word` to be a
string slice instead of a `String`, wouldn't it?? There is a way to add one character to line
9, though, that will coerce the `String` into a string slice."""

[[exercises]]
name = "strings3"
path = "exercises/strings/strings3.rs"
mode = "test"
hint = """
There's tons of useful standard library functions for strings. Let's try and use some of
them!

For the compose_me method: You can either use the `format!` macro, or convert the string
slice into an owned string, which you can then freely extend."""

[[exercises]]
name = "strings4"
path = "exercises/strings/strings4.rs"
mode = "compile"
hint = "No hints this time ;)"

# MODULES

[[exercises]]
name = "modules1"
path = "exercises/modules/modules1.rs"
mode = "compile"
hint = """
Everything is private in Rust by default-- but there's a keyword we can use
to make something public! The compiler error should point to the thing that
needs to be public."""

[[exercises]]
name = "modules2"
path = "exercises/modules/modules2.rs"
mode = "compile"
hint = """
The delicious_snacks module is trying to present an external interface that is 
different than its internal structure (the `fruits` and `veggies` modules and
associated constants). Complete the `use` statements to fit the uses in main and
find the one keyword missing for both constants."""

[[exercises]]
name = "modules3"
path = "exercises/modules/modules3.rs"
mode = "compile"
hint = """
UNIX_EPOCH and SystemTime are declared in the std::time module. Add a use statement
for these two to bring them into scope. You can use nested paths or the glob
operator to bring these two in using only one line."""

# HASHMAPS

[[exercises]]
name = "hashmaps1"
path = "exercises/hashmaps/hashmaps1.rs"
mode = "test"
hint = """
Hint 1: Take a look at the return type of the function to figure out
  the type for the `basket`.
Hint 2: Number of fruits should be at least 5. And you have to put
  at least three different types of fruits.
"""

[[exercises]]
name = "hashmaps2"
path = "exercises/hashmaps/hashmaps2.rs"
mode = "test"
hint = """
Use the `entry()` and `or_insert()` methods of `HashMap` to achieve this.
Learn more at https://doc.rust-lang.org/stable/book/ch08-03-hash-maps.html#only-inserting-a-value-if-the-key-has-no-value
"""

[[exercises]]
name = "hashmaps3"
path = "exercises/hashmaps/hashmaps3.rs"
mode = "test"
hint = """
Hint 1: Use the `entry()` and `or_insert()` methods of `HashMap` to insert entries corresponding to each team in the scores table.
Learn more at https://doc.rust-lang.org/stable/book/ch08-03-hash-maps.html#only-inserting-a-value-if-the-key-has-no-value
Hint 2: If there is already an entry for a given key, the value returned by `entry()` can be updated based on the existing value.
Learn more at https://doc.rust-lang.org/book/ch08-03-hash-maps.html#updating-a-value-based-on-the-old-value
"""

# QUIZ 2

[[exercises]]
name = "quiz2"
path = "exercises/quiz2.rs"
mode = "test"
hint = "No hints this time ;)"

# OPTIONS

[[exercises]]
name = "options1"
path = "exercises/options/options1.rs"
mode = "test"
hint = """
Options can have a Some value, with an inner value, or a None value, without an inner value.
There's multiple ways to get at the inner value, you can use unwrap, or pattern match. Unwrapping
is the easiest, but how do you do it safely so that it doesn't panic in your face later?"""

[[exercises]]
name = "options2"
path = "exercises/options/options2.rs"
mode = "compile"
hint = """
check out:
https://doc.rust-lang.org/rust-by-example/flow_control/if_let.html
https://doc.rust-lang.org/rust-by-example/flow_control/while_let.html

Remember that Options can be stacked in if let and while let.
For example: Some(Some(variable)) = variable2
Also see Option::flatten
"""

[[exercises]]
name = "options3"
path = "exercises/options/options3.rs"
mode = "compile"
hint = """
The compiler says a partial move happened in the `match`
statement. How can this be avoided? The compiler shows the correction
needed. After making the correction as suggested by the compiler, do
read: https://doc.rust-lang.org/std/keyword.ref.html"""

# ERROR HANDLING

[[exercises]]
name = "errors1"
path = "exercises/error_handling/errors1.rs"
mode = "test"
hint = """
`Ok` and `Err` are one of the variants of `Result`, so what the tests are saying
is that `generate_nametag_text` should return a `Result` instead of an
`Option`.

To make this change, you'll need to:
   - update the return type in the function signature to be a Result<String, String> that
     could be the variants `Ok(String)` and `Err(String)`
   - change the body of the function to return `Ok(stuff)` where it currently
     returns `Some(stuff)`
   - change the body of the function to return `Err(error message)` where it
     currently returns `None`"""

[[exercises]]
name = "errors2"
path = "exercises/error_handling/errors2.rs"
mode = "test"
hint = """
One way to handle this is using a `match` statement on
`item_quantity.parse::<i32>()` where the cases are `Ok(something)` and
`Err(something)`. This pattern is very common in Rust, though, so there's
a `?` operator that does pretty much what you would make that match statement
do for you! Take a look at this section of the Error Handling chapter:
https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator
and give it a try!"""

[[exercises]]
name = "errors3"
path = "exercises/error_handling/errors3.rs"
mode = "compile"
hint = """
If other functions can return a `Result`, why shouldn't `main`? It's a fairly common
convention to return something like Result<(), ErrorType> from your main function.
The unit (`()`) type is there because nothing is really needed in terms of positive
results."""

[[exercises]]
name = "errors4"
path = "exercises/error_handling/errors4.rs"
mode = "test"
hint = """
`PositiveNonzeroInteger::new` is always creating a new instance and returning an `Ok` result.
It should be doing some checking, returning an `Err` result if those checks fail, and only
returning an `Ok` result if those checks determine that everything is... okay :)"""

[[exercises]]
name = "errors5"
path = "exercises/error_handling/errors5.rs"
mode = "compile"
hint = """
There are two different possible `Result` types produced within `main()`, which are
propagated using `?` operators. How do we declare a return type from `main()` that allows both? 

Under the hood, the `?` operator calls `From::from` on the error value to convert it to a boxed
trait object, a `Box<dyn error::Error>`. This boxed trait object is polymorphic, and since all
errors implement the `error:Error` trait, we can capture lots of different errors in one "Box" 
object. 

Check out this section of the book:
https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator

Read more about boxing errors:
https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/boxing_errors.html

Read more about using the `?` operator with boxed errors:
https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/reenter_question_mark.html
"""

[[exercises]]
name = "errors6"
path = "exercises/error_handling/errors6.rs"
mode = "test"
hint = """
This exercise uses a completed version of `PositiveNonzeroInteger` from
errors4.

Below the line that TODO asks you to change, there is an example of using
the `map_err()` method on a `Result` to transform one type of error into
another. Try using something similar on the `Result` from `parse()`. You
might use the `?` operator to return early from the function, or you might
use a `match` expression, or maybe there's another way!

You can create another function inside `impl ParsePosNonzeroError` to use
with `map_err()`.

Read more about `map_err()` in the `std::result` documentation:
https://doc.rust-lang.org/std/result/enum.Result.html#method.map_err"""

# Generics

[[exercises]]
name = "generics1"
path = "exercises/generics/generics1.rs"
mode = "compile"
hint = """
Vectors in rust make use of generics to create dynamically sized arrays of any type.
You need to tell the compiler what type we are pushing onto this vector."""

[[exercises]]
name = "generics2"
path = "exercises/generics/generics2.rs"
mode = "test"
hint = """
Currently we are wrapping only values of type 'u32'.
Maybe we could update the explicit references to this data type somehow?

If you are still stuck https://doc.rust-lang.org/stable/book/ch10-01-syntax.html#in-method-definitions
"""

# TRAITS

[[exercises]]
name = "traits1"
path = "exercises/traits/traits1.rs"
mode = "test"
hint = """
A discussion about Traits in Rust can be found at:
https://doc.rust-lang.org/book/ch10-02-traits.html
"""

[[exercises]]
name = "traits2"
path = "exercises/traits/traits2.rs"
mode = "test"
hint = """
Notice how the trait takes ownership of 'self',and returns `Self'.
Try mutating the incoming string vector. Have a look at the tests to see
what the result should look like!

Vectors provide suitable methods for adding an element at the end. See
the documentation at: https://doc.rust-lang.org/std/vec/struct.Vec.html"""

# QUIZ 3

[[exercises]]
name = "quiz3"
path = "exercises/quiz3.rs"
mode = "test"
hint = """
To find the best solution to this challenge you're going to need to think back to your
knowledge of traits, specifically Trait Bound Syntax -  you may also need this: "use std::fmt::Display;""""

# TESTS

[[exercises]]
name = "tests1"
path = "exercises/tests/tests1.rs"
mode = "test"
hint = """
You don't even need to write any code to test -- you can just test values and run that, even
though you wouldn't do that in real life :) `assert!` is a macro that needs an argument.
Depending on the value of the argument, `assert!` will do nothing (in which case the test will
pass) or `assert!` will panic (in which case the test will fail). So try giving different values
to `assert!` and see which ones compile, which ones pass, and which ones fail :)"""

[[exercises]]
name = "tests2"
path = "exercises/tests/tests2.rs"
mode = "test"
hint = """
Like the previous exercise, you don't need to write any code to get this test to compile and
run. `assert_eq!` is a macro that takes two arguments and compares them. Try giving it two
values that are equal! Try giving it two arguments that are different! Try giving it two values
that are of different types! Try switching which argument comes first and which comes second!"""

[[exercises]]
name = "tests3"
path = "exercises/tests/tests3.rs"
mode = "test"
hint = """
You can call a function right where you're passing arguments to `assert!` -- so you could do
something like `assert!(having_fun())`. If you want to check that you indeed get false, you
can negate the result of what you're doing using `!`, like `assert!(!having_fun())`."""

# STANDARD LIBRARY TYPES

[[exercises]]
name = "iterators1"
path = "exercises/standard_library_types/iterators1.rs"
mode = "compile"
hint = """
Step 1:
We need to apply something to the collection `my_fav_fruits` before we start to go through
it. What could that be? Take a look at the struct definition for a vector for inspiration:
https://doc.rust-lang.org/std/vec/struct.Vec.html.
Step 2 & step 2.1:
Very similar to the lines above and below. You've got this!
Step 3:
An iterator goes through all elements in a collection, but what if we've run out of
elements? What should we expect here? If you're stuck, take a look at
https://doc.rust-lang.org/std/iter/trait.Iterator.html for some ideas.
"""

[[exercises]]
name = "iterators2"
path = "exercises/standard_library_types/iterators2.rs"
mode = "test"
hint = """
Step 1
The variable `first` is a `char`. It needs to be capitalized and added to the
remaining characters in `c` in order to return the correct `String`.
The remaining characters in `c` can be viewed as a string slice using the
`as_str` method.
The documentation for `char` contains many useful methods.
https://doc.rust-lang.org/std/primitive.char.html

Step 2
Create an iterator from the slice. Transform the iterated values by applying
the `capitalize_first` function. Remember to collect the iterator.

Step 3.
This is surprising similar to the previous solution. Collect is very powerful
and very general. Rust just needs to know the desired type."""

[[exercises]]
name = "iterators3"
path = "exercises/standard_library_types/iterators3.rs"
mode = "test"
hint = """
The divide function needs to return the correct error when even division is not
possible.

The division_results variable needs to be collected into a collection type.

The result_with_list function needs to return a single Result where the success
case is a vector of integers and the failure case is a DivisionError.

The list_of_results function needs to return a vector of results.

See https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.collect for how 
the `FromIterator` trait is used in `collect()`. This trait is REALLY powerful! It
can make the solution to this exercise infinitely easier."""

[[exercises]]
name = "iterators4"
path = "exercises/standard_library_types/iterators4.rs"
mode = "test"
hint = """
In an imperative language, you might write a for loop that updates
a mutable variable. Or, you might write code utilizing recursion
and a match clause. In Rust you can take another functional
approach, computing the factorial elegantly with ranges and iterators.

Hint 2: Check out the `fold` and `rfold` methods!"""

[[exercises]]
name = "iterators5"
path = "exercises/standard_library_types/iterators5.rs"
mode = "test"
hint = """
The documentation for the std::iter::Iterator trait contains numerous methods
that would be helpful here.

Return 0 from count_collection_iterator to make the code compile in order to
test count_iterator.

The collection variable in count_collection_iterator is a slice of HashMaps. It
needs to be converted into an iterator in order to use the iterator methods.

The fold method can be useful in the count_collection_iterator function.

For a further challenge, consult the documentation for Iterator to find
a different method that could make your code more compact than using fold."""

[[exercises]]
name = "box1"
path = "exercises/standard_library_types/box1.rs"
mode = "test"
hint = """
Step 1
The compiler's message should help: since we cannot store the value of the actual type
when working with recursive types, we need to store a reference (pointer) to its value.
We should, therefore, place our `List` inside a `Box`. More details in the book here:
https://doc.rust-lang.org/book/ch15-01-box.html#enabling-recursive-types-with-boxes

Step 2
Creating an empty list should be fairly straightforward (hint: peek at the assertions).
For a non-empty list keep in mind that we want to use our Cons "list builder".
Although the current list is one of integers (i32), feel free to change the definition
and try other types!
"""

[[exercises]]
name = "arc1"
path = "exercises/standard_library_types/arc1.rs"
mode = "compile"
hint = """
Make `shared_numbers` be an `Arc` from the numbers vector. Then, in order
to avoid creating a copy of `numbers`, you'll need to create `child_numbers`
inside the loop but still in the main thread.

`child_numbers` should be a clone of the Arc of the numbers instead of a
thread-local copy of the numbers.

This is a simple exercise if you understand the underlying concepts, but if this
is too much of a struggle, consider reading through all of Chapter 16 in the book:
https://doc.rust-lang.org/stable/book/ch16-00-concurrency.html
"""

# THREADS

[[exercises]]
name = "threads1"
path = "exercises/threads/threads1.rs"
mode = "compile"
hint = """
`JoinHandle` is a struct that is returned from a spawned thread: 
https://doc.rust-lang.org/std/thread/fn.spawn.html

A challenge with multi-threaded applications is that the main thread can 
finish before the spawned threads are completed.
https://doc.rust-lang.org/book/ch16-01-threads.html#waiting-for-all-threads-to-finish-using-join-handle

Collect the JoinHandles and wait for them to finish.
https://doc.rust-lang.org/std/thread/struct.JoinHandle.html
"""

[[exercises]]
name = "threads2"
path = "exercises/threads/threads2.rs"
mode = "compile"
hint = """
`Arc` is an Atomic Reference Counted pointer that allows safe, shared access
to **immutable** data. But we want to *change* the number of `jobs_completed`
so we'll need to also use another type that will only allow one thread to
mutate the data at a time. Take a look at this section of the book:
https://doc.rust-lang.org/book/ch16-03-shared-state.html#atomic-reference-counting-with-arct
and keep reading if you'd like more hints :)


Do you now have an `Arc` `Mutex` `JobStatus` at the beginning of main? Like:
`let status = Arc::new(Mutex::new(JobStatus { jobs_completed: 0 }));`
Similar to the code in the example in the book that happens after the text
that says "We can use Arc<T> to fix this.". If not, give that a try! If you
do and would like more hints, keep reading!!


Make sure neither of your threads are holding onto the lock of the mutex
while they are sleeping, since this will prevent the other thread from
being allowed to get the lock. Locks are automatically released when
they go out of scope.

If you've learned from the sample solutions, I encourage you to come
back to this exercise and try it again in a few days to reinforce
what you've learned :)"""

# MACROS

[[exercises]]
name = "macros1"
path = "exercises/macros/macros1.rs"
mode = "compile"
hint = """
When you call a macro, you need to add something special compared to a
regular function call. If you're stuck, take a look at what's inside
`my_macro`."""

[[exercises]]
name = "macros2"
path = "exercises/macros/macros2.rs"
mode = "compile"
hint = """
Macros don't quite play by the same rules as the rest of Rust, in terms of
what's available where.

Unlike other things in Rust, the order of "where you define a macro" versus
"where you use it" actually matters."""

[[exercises]]
name = "macros3"
path = "exercises/macros/macros3.rs"
mode = "compile"
hint = """
In order to use a macro outside of its module, you need to do something
special to the module to lift the macro out into its parent.

The same trick also works on "extern crate" statements for crates that have
exported macros, if you've seen any of those around."""

[[exercises]]
name = "macros4"
path = "exercises/macros/macros4.rs"
mode = "compile"
hint = """
You only need to add a single character to make this compile.
The way macros are written, it wants to see something between each
"macro arm", so it can separate them.

That's all the macro exercises we have in here, but it's barely even
scratching the surface of what you can do with Rust's macros. For a more
thorough introduction, you can have a read through the little book of Rust
macros: https://veykril.github.io/tlborm/"""

#  CLIPPY

[[exercises]]
name = "clippy1"
path = "exercises/clippy/clippy1.rs"
mode = "clippy"
hint = """
Rust stores the highest precision version of any long or inifinite precision
mathematical constants in the rust standard library.
https://doc.rust-lang.org/stable/std/f32/consts/index.html

We may be tempted to use our own approximations for certain mathematical constants,
but clippy recognizes those imprecise mathematical constants as a source of 
potential error.
See the suggestions of the clippy warning in compile output and use the
appropriate replacement constant from std::f32::consts..."""

[[exercises]]
name = "clippy2"
path = "exercises/clippy/clippy2.rs"
mode = "clippy"
hint = """
`for` loops over Option values are more clearly expressed as an `if let`"""

[[exercises]]
name = "clippy3"
path = "exercises/clippy/clippy3.rs"
mode = "clippy"
hint = "No hints this time!"

# TYPE CONVERSIONS

[[exercises]]
name = "using_as"
path = "exercises/conversions/using_as.rs"
mode = "test"
hint = """
Use the `as` operator to cast one of the operands in the last line of the
`average` function into the expected return type."""

[[exercises]]
name = "from_into"
path = "exercises/conversions/from_into.rs"
mode = "test"
hint = """
Follow the steps provided right before the `From` implementation"""

[[exercises]]
name = "from_str"
path = "exercises/conversions/from_str.rs"
mode = "test"
hint = """
The implementation of FromStr should return an Ok with a Person object,
or an Err with an error if the string is not valid.

This is almost like the `from_into` exercise, but returning errors instead
of falling back to a default value.

Look at the test cases to see which error variants to return.

Another hint: You can use the `map_err` method of `Result` with a function
or a closure to wrap the error from `parse::<usize>`.

Yet another hint: If you would like to propagate errors by using the `?`
operator in your solution, you might want to look at
https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/reenter_question_mark.html
"""

[[exercises]]
name = "try_from_into"
path = "exercises/conversions/try_from_into.rs"
mode = "test"
hint = """
Follow the steps provided right before the `TryFrom` implementation.
You can also use the example at https://doc.rust-lang.org/std/convert/trait.TryFrom.html

Is there an implementation of `TryFrom` in the standard library that
can both do the required integer conversion and check the range of the input?

Another hint: Look at the test cases to see which error variants to return.

Yet another hint: You can use the `map_err` or `or` methods of `Result` to
convert errors.

Yet another hint: If you would like to propagate errors by using the `?`
operator in your solution, you might want to look at
https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/reenter_question_mark.html

Challenge: Can you make the `TryFrom` implementations generic over many integer types?"""

[[exercises]]
name = "as_ref_mut"
path = "exercises/conversions/as_ref_mut.rs"
mode = "test"
hint = """
Add AsRef<str> as a trait bound to the functions."""