//@ `[T]` is the type of an (unsized) *array*, with elements of type `T`. All this means is that there's a contiguous
//@ region of memory, where a bunch of `T` are stored. How many? We can't tell! This is an unsized type. Just like for
//@ trait objects, this means we can only operate on pointers to that type, and these pointers will carry the missing
-//@ information - namely, the length. Such a pointer is called a *slice*. As we will see, a slice can be split.
-//@ Our function can thus take a borrowed slice, and promise to sort all elements in there.
+//@ information - namely, the length (they will be *fat pointers*). Such a reference to an array is called a *slice*. As we will see, a slice can be split.
+//@ Our function can thus take a mutable slice, and promise to sort all elements in there.
pub fn sort<T: PartialOrd>(data: &mut [T]) {
if data.len() < 2 { return; }
/* Invariant: pivot is data[0]; everything with index (0,lpos) is <= pivot;
[rpos,len) is >= pivot; lpos < rpos */
loop {
- // **Exercise 13.1**: Complete this Quicksort loop. You can use `swap` on slices to swap two elements. Write a
+ // **Exercise 14.1**: Complete this Quicksort loop. You can use `swap` on slices to swap two elements. Write a
// test function for `sort`.
unimplemented!()
}
// Finally, we split our slice to sort the two halves. The nice part about slices is that splitting them is cheap:
//@ They are just a pointer to a start address, and a length. We can thus get two pointers, one at the beginning and
//@ one in the middle, and set the lengths appropriately such that they don't overlap. This is what `split_at_mut` does.
- //@ Since the two slices don't overlap, there is no aliasing and we can have them both mutably borrowed.
+ //@ Since the two slices don't overlap, there is no aliasing and we can have both of them as unique, mutable slices.
let (part1, part2) = data.split_at_mut(lpos);
//@ The index operation can not only be used to address certain elements, it can also be used for *slicing*: Giving a range
//@ of indices, and obtaining an appropriate part of the slice we started with. Here, we remove the last element from
sort(part2); /*@*/
}
-// **Exercise 13.2**: Since `String` implements `PartialEq`, you can now change the function `output_lines` in the previous part
-// to call the sort function above. If you did exercise 12.1, you will have slightly more work. Make sure you sort by the matched line
+// **Exercise 14.2**: Since `String` implements `PartialEq`, you can now change the function `output_lines` in the previous part
+// to call the sort function above. If you did exercise 13.1, you will have slightly more work. Make sure you sort by the matched line
// only, not by filename or line number!
// Now, we can sort, e.g., an vector of numbers.
}
// ## Arrays
-//@ An *array* in Rust is given be the type `[T; n]`, where `n` is some *fixed* number. So, `[f64; 10]` is an array of 10 floating-point
+//@ An *array* in Rust is given by the type `[T; n]`, where `n` is some *fixed* number. So, `[f64; 10]` is an array of 10 floating-point
//@ numbers, all one right next to the other in memory. Arrays are sized, and hence can be used like any other type. But we can also
//@ borrow them as slices, e.g., to sort them.
fn sort_array() {
// ## External Dependencies
//@ This leaves us with just one more piece to complete rgrep: Taking arguments from the command-line. We could now directly work on
-//@ [`std::env::args`](http://doc.rust-lang.org/stable/std/env/fn.args.html) to gain access to those arguments, and this would become
+//@ [`std::env::args`](https://doc.rust-lang.org/stable/std/env/fn.args.html) to gain access to those arguments, and this would become
//@ a pretty boring lesson in string manipulation. Instead, I want to use this opportunity to show how easy it is to benefit from
//@ other people's work in your program.
//@
//@ arguments based on the usage string. External dependencies are declared in the `Cargo.toml` file.
//@ I already prepared that file, but the declaration of the dependency is still commented out. So please open `Cargo.toml` of your workspace
-//@ now, and enabled the two commented-out lines. Then do `cargo build`. Cargo will now download the crate from crates.io, compile it,
+//@ now, and enable the two commented-out lines. Then do `cargo build`. Cargo will now download the crate from crates.io, compile it,
//@ and link it to your program. In the future, you can do `cargo update` to make it download new versions of crates you depend on.
//@ Note that crates.io is only the default location for dependencies, you can also give it the URL of a git repository or some local
//@ path. All of this is explained in the [Cargo Guide](http://doc.crates.io/guide.html).
// Remove the attribute of the `rgrep` module to enable compilation.
#[cfg(feature = "disabled")]
pub mod rgrep {
- // Now that `docopt` is linked, we can first add it to the namespace and then import shorter names with `use`. We also import some other pieces that we will need.
+ // Now that `docopt` is linked, we can first add it to the namespace with `extern crate` and then import shorter names with `use`.
+ // We also import some other pieces that we will need.
extern crate docopt;
use self::docopt::Docopt;
- use part12::{run, Options, OutputMode};
+ use part13::{run, Options, OutputMode};
use std::process;
// The `USAGE` string documents how the program is to be called. It's written in a format that `docopt` can parse.
// This function extracts the rgrep options from the command-line arguments.
fn get_options() -> Options {
- // Parse `argv` and exit the program with an error message if it fails. This is taken from the [`docopt` documentation](http://burntsushi.net/rustdoc/docopt/).
+ // This parses `argv` and exit the program with an error message if it fails. The code is taken from the [`docopt` documentation](http://burntsushi.net/rustdoc/docopt/). <br/>
//@ The function `and_then` takes a closure from `T` to `Result<U, E>`, and uses it to transform a `Result<T, E>` to a
//@ `Result<U, E>`. This way, we can chain computations that only happen if the previous one succeeded (and the error
//@ type has to stay the same). In case you know about monads, this style of programming will be familiar to you.
//@ encoded string, that is, a bunch of bytes in memory (`[u8]`) that are valid according of UTF-8. `str` is unsized. `&str`
//@ stores the address of the character data, and their length. String literals like "this one" are
//@ of type `&'static str`: They point right to the constant section of the binary, so
- //@ However, the borrow is valid for as long as the program runs, hence it has lifetime `'static`. Calling
- //@ `to_string` will copy the string data into an owned buffer on the heap, and thus convert it to `String`.
+ //@ the reference is valid for the entire program. The bytes pointed to by `pattern`, on the other hand, are owned by someone else,
+ //@ and we call `to_string` on it to copy the string data into a buffer on the heap that we own.
let mode = if count {
OutputMode::Count
} else if sort {
}
}
-// **Exercise 13.3**: Wouldn't it be nice if rgrep supported regular expressions? There's already a crate that does all the parsing and matching on regular
+// **Exercise 14.3**: Wouldn't it be nice if rgrep supported regular expressions? There's already a crate that does all the parsing and matching on regular
// expression, it's called [regex](https://crates.io/crates/regex). Add this crate to the dependencies of your workspace, add an option ("-r") to switch
// the pattern to regular-expression mode, and change `filter_lines` to honor this option. The documentation of regex is available from its crates.io site.
// (You won't be able to use the `regex!` macro if you are on the stable or beta channel of Rust. But it wouldn't help for our use-case anyway.)
-//@ [index](main.html) | [previous](part13.html) | [next](part15.html)
+//@ [index](main.html) | [previous](part13.html) | [raw source](https://www.ralfj.de/git/rust-101.git/blob_plain/HEAD:/workspace/src/part14.rs) | [next](part15.html)
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