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@@ -287,23 +287,24 @@ 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"
mode = "test"
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
When running this exercise for the first time, you'll notice an error about
"borrow of moved value". 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. When we pass `vec0` into `fill_vec`, it's being
"moved" into `vec1`, meaning we can't access `vec0` anymore after the fact.
Rust provides a couple of different ways to mitigate this issue, feel free to try them all:
1. You could 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!`"""
and then copy the data within the function (`vec.clone()`) in order to return an owned
`Vec<i32>`.
3. Or, you could make `fill_vec` *mutably* borrow a reference to its argument (which will need to be
mutable), modify it directly, then not return anything. This means that `vec0` will change over the
course of the function, and makes `vec1` redundant (make sure to change the parameters of the `println!`
statements if you go this route)
"""
[[exercises]]
name = "move_semantics3"
@@ -905,67 +906,6 @@ 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."""
# 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-handles
Use the JoinHandles to wait for each thread to finish and collect their results.
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 :)"""
[[exercises]]
name = "threads3"
path = "exercises/threads/threads3.rs"
mode = "compile"
hint = """
An alternate way to handle concurrency between threads is to use
a mpsc (multiple producer, single consumer) channel to communicate.
With both a sending end and a receiving end, it's possible to
send values in one thread and receive them in another.
Multiple producers are possible by using clone() to create a duplicate
of the original sending end.
See https://doc.rust-lang.org/book/ch16-02-message-passing.html for more info.
"""
# SMART POINTERS
[[exercises]]
@@ -1028,6 +968,67 @@ Check out https://doc.rust-lang.org/std/borrow/enum.Cow.html for documentation
on the `Cow` type.
"""
# 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-handles
Use the JoinHandles to wait for each thread to finish and collect their results.
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 :)"""
[[exercises]]
name = "threads3"
path = "exercises/threads/threads3.rs"
mode = "compile"
hint = """
An alternate way to handle concurrency between threads is to use
a mpsc (multiple producer, single consumer) channel to communicate.
With both a sending end and a receiving end, it's possible to
send values in one thread and receive them in another.
Multiple producers are possible by using clone() to create a duplicate
of the original sending end.
See https://doc.rust-lang.org/book/ch16-02-message-passing.html for more info.
"""
# MACROS
[[exercises]]
@@ -1170,4 +1171,4 @@ name = "as_ref_mut"
path = "exercises/conversions/as_ref_mut.rs"
mode = "test"
hint = """
Add AsRef<str> as a trait bound to the functions."""
Add AsRef<str> or AsMut<u32> as a trait bound to the functions."""