Merge pull request #1244 from black-puppydog/cow-rework
refactor(cow1): replace main with tests
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216d08d013
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@ -4,6 +4,9 @@
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// Cow is a clone-on-write smart pointer.
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// It can enclose and provide immutable access to borrowed data, and clone the data lazily when mutation or ownership is required.
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// The type is designed to work with general borrowed data via the Borrow trait.
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//
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// This exercise is meant to show you what to expect when passing data to Cow.
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// Fix the unit tests by checking for Cow::Owned(_) and Cow::Borrowed(_) at the TODO markers.
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// I AM NOT DONE
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@ -20,29 +23,52 @@ fn abs_all<'a, 'b>(input: &'a mut Cow<'b, [i32]>) -> &'a mut Cow<'b, [i32]> {
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input
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}
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fn main() {
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// No clone occurs because `input` doesn't need to be mutated.
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let slice = [0, 1, 2];
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let mut input = Cow::from(&slice[..]);
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match abs_all(&mut input) {
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Cow::Borrowed(_) => println!("I borrowed the slice!"),
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_ => panic!("expected borrowed value"),
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn reference_mutation() -> Result<(), &'static str> {
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// Clone occurs because `input` needs to be mutated.
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let slice = [-1, 0, 1];
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let mut input = Cow::from(&slice[..]);
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match abs_all(&mut input) {
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Cow::Owned(_) => Ok(()),
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_ => Err("Expected owned value"),
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}
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}
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// Clone occurs because `input` needs to be mutated.
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let slice = [-1, 0, 1];
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let mut input = Cow::from(&slice[..]);
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match abs_all(&mut input) {
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Cow::Owned(_) => println!("I modified the slice and now own it!"),
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_ => panic!("expected owned value"),
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#[test]
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fn reference_no_mutation() -> Result<(), &'static str> {
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// No clone occurs because `input` doesn't need to be mutated.
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let slice = [0, 1, 2];
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let mut input = Cow::from(&slice[..]);
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match abs_all(&mut input) {
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// TODO
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}
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}
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// No clone occurs because `input` is already owned.
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let slice = vec![-1, 0, 1];
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let mut input = Cow::from(slice);
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match abs_all(&mut input) {
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// TODO
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Cow::Borrowed(_) => println!("I own this slice!"),
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_ => panic!("expected borrowed value"),
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#[test]
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fn owned_no_mutation() -> Result<(), &'static str> {
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// We can also pass `slice` without `&` so Cow owns it directly.
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// In this case no mutation occurs and thus also no clone,
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// but the result is still owned because it always was.
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let slice = vec![0, 1, 2];
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let mut input = Cow::from(slice);
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match abs_all(&mut input) {
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// TODO
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}
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}
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#[test]
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fn owned_mutation() -> Result<(), &'static str> {
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// Of course this is also the case if a mutation does occur.
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// In this case the call to `to_mut()` returns a reference to
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// the same data as before.
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let slice = vec![-1, 0, 1];
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let mut input = Cow::from(slice);
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match abs_all(&mut input) {
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// TODO
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}
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}
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}
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@ -1010,11 +1010,11 @@ https://doc.rust-lang.org/stable/book/ch16-00-concurrency.html
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[[exercises]]
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name = "cow1"
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path = "exercises/smart_pointers/cow1.rs"
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mode = "compile"
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mode = "test"
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hint = """
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Since the vector is already owned, the `Cow` type doesn't need to clone it.
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If Cow already owns the data it doesn't need to clone it when to_mut() is called.
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Checkout https://doc.rust-lang.org/std/borrow/enum.Cow.html for documentation
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Check out https://doc.rust-lang.org/std/borrow/enum.Cow.html for documentation
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on the `Cow` type.
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"""
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