Adds file_io1-3 (and their solutions) to dev/Cargo.toml's bin list so
'cargo dev check'/'cargo dev update' pick them up, and registers them in
rustlings-macros/info.toml with hints that explain each exercise's
learning goal and point at the relevant std API.
Adds three new exercises under exercises/24_file_io/, as proposed in rust-lang/rustlings#2233:
- file_io1: read a whole file with fs::read_to_string and handle the Result.
- file_io2: read/write a file efficiently with BufReader/BufWriter.
- file_io3: build a path with PathBuf and inspect it with .metadata().
Includes matching solutions and a README describing the learning goal of
each exercise.
To understand From-based conversion, an understanding of traits is
required, which we teach in a later chapter. The From trait specifically
is taught in one of the conversion exercises. So, we can safely remove
it here without users missing out on learning something important.
A specific source of confusion for users was a warning that the
conversion is useless, which appeared when using the `string_slice`
function for the expression with `.into()`. closes#2190
Conversion between Celsius and Fahrenheit should be understandable to
most. Inverting the formula is still not very hard, but a little harder
than only multiplying by 100.
Learners were sometimes confused by the literal array. Their assumption
was that they are supposed to convert the array to a vector. Duplicating
the literal elements was not an intuitive solution.
This redesign avoids putting an identical array literal near the place
where learners are supposed to use the vec! macro.
This was discussed in another PR, but it was merged before the code was
updated to the most recent consensus:
https://github.com/rust-lang/rustlings/pull/2353
Co-authored-by: Piotr Spieker <p.spieker@posteo.de>
This avoids confusion between `.into_iter()` and `.iter()`. On a slice,
both methods do the same (correct) thing. Using `.into_iter()` will
result in a clippy warning about the slice not being consumed.
