rustlings/info.toml

# VARIABLES

[[exercises]]
name = "variables1"
path = "exercises/variables/variables1.rs"
mode = "compile"
hint = """
Hint: The declaration on line 12 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 = """
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 = "variables4"
path = "exercises/variables/variables4.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 = "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 
then keyword 'let'.
Constants types must also always be annotated.

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

# 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 return the same type! To get the tests passing, you will need a couple
conditions checking different input values."""

# 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."""

[[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!"""

[[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 its operand, 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`"""

# TEST 1

[[exercises]]
name = "test1"
path = "exercises/test1.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 Deref coercions section of the book:
https://doc.rust-lang.org/book/ch15-02-deref.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 = "compile"
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!"""

# STRUCTS

[[exercises]]
name = "structs1"
path = "exercises/structs/structs1.rs"
mode = "test"
hint = """
Rust has more than one type of struct. Both variants are used to package related data together.
On the one hand, there are normal, or classic, structs. These are named collections of related data stored in fields.
The other variant is tuple structs. Basically just named tuples.
In this exercise you need to implement one of each kind.

Read more about structs in The Book: https://doc.rust-lang.org/stable/book/ch05-00-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 is 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"""

# 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."""

# TEST 2

[[exercises]]
name = "test2"
path = "exercises/test2.rs"
mode = "compile"
hint = "No hints this time ;)"

# ENUMS

[[exercises]]
name = "enums1"
path = "exercises/enums/enums1.rs"
mode = "compile"
hint = """
Hint: The declaration of the enumeration type has not been defined yet."""

[[exercises]]
name = "enums2"
path = "exercises/enums/enums2.rs"
mode = "compile"
hint = """
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 = "No hints this time ;)"

# 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())`."""

# TEST 3

[[exercises]]
name = "test3"
path = "exercises/test3.rs"
mode = "test"
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 (the `fruit` and `veggie` constants) that is different than
its internal structure (the `fruits` and `veggies` modules and
associated constants). It's almost there except for one keyword missing for
each constant."""

# 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."""
# TEST 4

[[exercises]]
name = "test4"
path = "exercises/test4.rs"
mode = "test"
hint = "No hints this time ;)"

# 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."""

[[exercises]]
name = "move_semantics2"
path = "exercises/move_semantics/move_semantics2.rs"
mode = "compile"
hint = """
So `vec0` is being *moved* into the function `fill_vec` when we call it on
line 10, which means it gets dropped at the end of `fill_vec`, which means we
can't use `vec0` again on line 13 (or anywhere else in `main` after the
`fill_vec` call for that matter). We could fix this in a few ways, try them
all!
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 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`"""

# ERROR HANDLING

[[exercises]]
name = "errors1"
path = "exercises/error_handling/errors1.rs"
mode = "test"
hint = """
`Err` is one of the variants of `Result`, so what the 2nd test is 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`
   - change the first test to expect `Ok(stuff)` where it currently expects
     `Some(stuff)`."""

[[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 = "test"
hint = """
If other functions can return a `Result`, why shouldn't `main`?"""

[[exercises]]
name = "errorsn"
path = "exercises/error_handling/errorsn.rs"
mode = "test"
hint = """
First hint: To figure out what type should go where the ??? is, take a look
at the test helper function `test_with_str`, since it returns whatever
`read_and_validate` returns and `test_with_str` has its signature fully
specified.


Next hint: There are three places in `read_and_validate` that we call a
function that returns a `Result` (that is, the functions might fail).
Apply the `?` operator on those calls so that we return immediately from
`read_and_validate` if those function calls fail.


Another hint: 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>,
which is polymorphic-- that means that lots of different kinds of errors
can be returned from the same function because all errors act the same
since they all implement the `error::Error` trait.
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


Another another hint: Note that because the `?` operator returns
the *unwrapped* value in the `Ok` case, if we want to return a `Result` from
`read_and_validate` for *its* success case, we'll have to rewrap a value
that we got from the return value of a `?`ed call in an `Ok`-- this will
look like `Ok(something)`.


Another another another hint: `Result`s must be "used", that is, you'll
get a warning if you don't handle a `Result` that you get in your
function. Read more about that in the `std::result` module docs:
https://doc.rust-lang.org/std/result/#results-must-be-used"""

# OPTIONS / RESULTS

[[exercises]]
name = "option1"
path = "exercises/option/option1.rs"
mode = "compile"
hint = """
Check out some functions of Option:
is_some
is_none
unwrap

and:
pattern matching
"""

[[exercises]]
name = "option2"
path = "exercises/option/option2.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


"""

[[exercises]]
name = "result1"
path = "exercises/error_handling/result1.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 :)"""

#  CLIPPY

[[exercises]]
name = "clippy1"
path = "exercises/clippy/clippy1.rs"
mode = "clippy"
hint = """
Floating point calculations are usually imprecise, so asking if two values are exactly equal is asking for trouble"""

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

# STANDARD LIBRARY 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."""

[[exercises]]
name = "iterators2"
path = "exercises/standard_library_types/iterators2.rs"
mode = "test"
hint = """
Step 1
You need to call something on `first` before it can be collected
Currently its type is `char`. Have a look at the methods that are available on that type:
https://doc.rust-lang.org/std/primitive.char.html


Step 2
First you'll need to turn the Vec into an iterator
Then you'll need to apply your function unto each item in the vector
P.s. Don't forget to collect() at the end!


Step 3.
This is very similar to the previous test. The only real change is that you will need to
alter the type that collect is coerced into. For a bonus you could try doing this with a
turbofish"""

[[exercises]]
name = "iterators3"
path = "exercises/standard_library_types/iterators3.rs"
mode = "test"
hint = """
Minor hint: In each of the two cases in the match in main, you can create x with either
a 'turbofish' or by hinting the type of x to the compiler. You may try both.

Major hint: Have a look at the Iter trait and at the explanation of its collect function.
Especially the part about Result is interesting."""

[[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."""

# 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.

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"""

# 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 = """
Think carefully about what we need to do here. Currently we are wrapping only values of
type 'u32'. Maybe we need to update the explicit references to this data type somehow?
"""

[[exercises]]
name = "generics3"
path = "exercises/generics/generics3.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;"

This is definitely harder than the last two exercises! You need to think about not only making the
ReportCard struct generic, but also the correct property - you will need to change the implementation
of the struct slightly too...you can do it!
"""

# THREADS

[[exercises]]
name = "threads1"
path = "exercises/threads/threads1.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.

Ok, so, real talk, this was actually tricky for *me* to do too. And
I could see a lot of different problems you might run into, so at this
point I'm not sure which one you've hit :)

Please open an issue if you're still running into a problem that
these hints are not helping you with, or if you've looked at the sample
answers and don't understand why they work and yours doesn't.

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 :)"""

# TYPE CONVERSIONS

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

[[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."""

[[exercises]]
name = "from_str"
path = "exercises/conversions/from_str.rs"
mode = "test"
hint = """
If you've already solved try_from_into.rs, then this is almost a copy-paste.
Otherwise, go ahead and solve try_from_into.rs first."""