-* Arrays/slices
-* Arc, concurrency, channels: Some grep-like thing, "rgrep"
-* Send, Sync
-* External dependencies: regexp crate, add to rgrep
-
-* Shared-memoty concurrency, interior mutability: Concurrent counter
+* Shared-memoty concurrency, interior mutability, Sync: Concurrent counter
* Drop, unsafe: doubly-linked list
+// This crate contains solutions to *some* of the exercises, and it bundles
+// the projects that span multiple parts together in one file per project.
+// It is not always up-to-date with the code in the actual course, and mainly
+// serves as draft board for new parts or exercises.
+
extern crate docopt;
pub mod bigint;
fn run(options: Options) {
let options = Arc::new(options);
- // Set up the chain of threads. Use `sync_channel` with buffer-size of 16 to avoid needlessly filling RAM.
+ // This sets up the chain of threads. Use `sync_channel` with buffer-size of 16 to avoid needlessly filling RAM.
let (line_sender, line_receiver) = sync_channel(16);
let (filtered_sender, filtered_receiver) = sync_channel(16);
// * [Part 09: Iterators](part09.html)
// * [Part 10: Closures](part10.html)
// * [Part 11: Trait Objects, Box, Rc, Lifetime bounds](part11.html)
+// * [Part 12: Concurrency, Send](part12.html)
+// * [Part 13: Slices, Arrays, External Dependencies](part13.html)
// * (to be continued)
#![allow(dead_code, unused_imports, unused_variables, unused_mut, unreachable_code)]
/* extern crate docopt; */
//@ variable into the closure. Its environment will then contain a `usize` rather than a `&mut uszie`, and have
//@ no effect on this local variable anymore.
let mut count: usize = 0;
- c.register(Box::new(move |val| { count = count+1; println!("Callback 2, {}. time: {}", count, val); } ));
+ c.register(Box::new(move |val| {
+ count = count+1;
+ println!("Callback 2, {}. time: {}", count, val);
+ } ));
c.call(1); c.call(2);
}
}
//@ and do the creation of the `Rc` and the conversion to `Fn(i32)` itself.
//@ For this to work, we need to demand that the type `F` does not contain any short-lived borrows. After all, we will store it
- //@ in our list of callbacks indefinitely. `'static` is a lifetime, the lifetime of the entire program. We can use lifetimes
- //@ as bounds on types, to demand that anything in (an element of) the type lives at least as long as this lifetime. That bound was implicit in the `Box`
- //@ above, and it is the reason we could not have the borrowed `count` in the closure in `demo`.
+ //@ in our list of callbacks indefinitely. If the closure contained a pointer to our caller's stackframe, that pointer
+ //@ could be invalid by the time the closure is called. We can mitigate this by bounding `F` by a *lifetime*: `T: 'a` says
+ //@ that all data of type `T` will *outlive* (i.e., will be valid for at least as long as) lifetime `'a`.
+ //@ Here, we use the special lifetime `'static`, which is the lifetime of the entire program.
+ //@ The same bound has been implicitly added in the version of `register` above, and in the definition of
+ //@ `Callbacks`. This is the reason we could not have the borrowed `count` in the closure in `demo` previously.
pub fn register<F: Fn(i32)+'static>(&mut self, callback: F) {
self.callbacks.push(Rc::new(callback)); /*@*/
}
//@ than one version per type it is instantiated with). This makes for smaller code, but you pay the overhead of the virtual function calls.
//@ Isn't it beautiful how traits can handle both of these cases (and much more, as we saw, like closures and operator overloading) nicely?
-//@ [index](main.html) | [previous](part10.html) | [next](main.html)
+//@ [index](main.html) | [previous](part10.html) | [next](part12.html)
-// Rust-101, Part 12: Concurrency (WIP)
-// =================
+// Rust-101, Part 12: Concurrency, Send
+// ====================================
use std::io::prelude::*;
use std::{io, fs, thread};
use std::sync::mpsc::{sync_channel, SyncSender, Receiver};
use std::sync::Arc;
-//@ This part is introducing the concurrency features of Rust. We are going to write our own small version of "grep",
-//@ called *rgrep*, and it is going to make use of multiple cores: One thread reads the input files, one thread does
-//@ the actual matching, and one thread writes the output.
+//@ Our next stop are the concurrency features of Rust. We are going to write our own small version of "grep",
+//@ called *rgrep*, and it is going to make use of concurrency: One thread reads the input files, one thread does
+//@ the actual matching, and one thread writes the output. I already mentioned in the beginning of the course that
+//@ Rust's type system (more precisely, the discipline of ownership and borrowing) will help us to avoid a common
+//@ pitfall of concurrent programming: data races.
// Before we come to the actual code, we define a data-structure `Options` to store all the information we need
// to complete the job: Which files to work on, which pattern to look for, and how to output. <br/>
-// Besides just printing all the matching lines, we will also offer to count them, or alternatively to sort them.
+//@ Besides just printing all the matching lines, we will also offer to count them, or alternatively to sort them.
#[derive(Clone,Copy)]
pub enum OutputMode {
Print,
//@ Now we can write three functions to do the actual job of reading, matching, and printing, respectively.
//@ To get the data from one thread to the next, we will use *message passing*: We will establish communication
-//@ channels between the threads, with one thread *sending* data, and the other one receiving it. `SyncSender<T>`
+//@ channels between the threads, with one thread *sending* data, and the other one *receiving* it. `SyncSender<T>`
//@ is the type of the sending end of a synchronous channel transmitting data of type `T`. *Synchronous* here
//@ means that the `send` operation could block, waiting for the other side to make progress. We don't want to
-//@ end up with the entire files being stored in the buffer of the channels, and the output not being fast enough
+//@ end up with the entire file being stored in the buffer of the channels, and the output not being fast enough
//@ to keep up with the speed of input.
//@
//@ We also need all the threads to have access to the options of the job they are supposed to do. Since it would
//@ be rather unnecessary to actually copy these options around, we will use reference-counting to share them between
-//@ all threads. `Arc` is the thread-safe version of `Rc, using atomic operations to keep the reference count up-to-date.
-//@ You can also think of this as saying that *all* threads own the `Options` "a bit" - and since there could be other
-//@ owners, `Arc` (just like `Rc`) only permits read-only access to its content. That's good enough for the options, though.
+//@ all threads. `Arc` is the thread-safe version of `Rc`, using atomic operations to keep the reference count up-to-date.
-// The first functions reads the files, and sends every line over the `out_channel`.
+// The first function reads the files, and sends every line over the `out_channel`.
fn read_files(options: Arc<Options>, out_channel: SyncSender<String>) {
for file in options.files.iter() {
// First, we open the file, ignoring any errors.
// The second function filters the lines it receives through `in_channel` with the pattern, and sends
// matches via `out_channel`.
-fn filter_lines(options: Arc<Options>, in_channel: Receiver<String>, out_channel: SyncSender<String>) {
+fn filter_lines(options: Arc<Options>,
+ in_channel: Receiver<String>,
+ out_channel: SyncSender<String>) {
// We can simply iterate over the channel, which will stop when the channel is closed.
for line in in_channel.iter() {
// `contains` works on lots of types of patterns, but in particular, we can use it to test whether
- // one string is contained in another.
+ // one string is contained in another. This is another example of Rust using traits as substitute for overloading.
if line.contains(&options.pattern) {
out_channel.send(line).unwrap(); /*@*/
}
// We move the `options` into an `Arc`, as that's what the thread workers expect.
let options = Arc::new(options);
- // Set up the channels. Use `sync_channel` with buffer-size of 16 to avoid needlessly filling RAM.
+ // This sets up the channels. We use a `sync_channel` with buffer-size of 16 to avoid needlessly filling RAM.
let (line_sender, line_receiver) = sync_channel(16);
let (filtered_sender, filtered_receiver) = sync_channel(16);
// Same with the filter thread.
let options2 = options.clone();
- let handle2 = thread::spawn(move || filter_lines(options2, line_receiver, filtered_sender));
+ let handle2 = thread::spawn(move || {
+ filter_lines(options2, line_receiver, filtered_sender)
+ });
// And the output thread.
let options3 = options.clone();
//@ We need to call `to_string` on string literals to convert them to a fully-owned `String`.
pub fn main() {
let options = Options {
- files: vec!["src/part10.rs".to_string(), "src/part11.rs".to_string(), "src/part12.rs".to_string()],
+ files: vec!["src/part10.rs".to_string(),
+ "src/part11.rs".to_string(),
+ "src/part12.rs".to_string()],
pattern: "let".to_string(),
output_mode: Print
};
run(options);
}
-// **Exercise 12.1**: Change rgrep such that it prints now only the matching lines, but also the name of the file
+// **Exercise 12.1**: Change rgrep such that it prints not only the matching lines, but also the name of the file
// and the number of the line in the file. You will have to change the type of the channels from `String` to something
// that records this extra information.
//@ ## Ownership, Borrowing, and Concurrency
-//@ The little demo above showed that concurrency in Rust has a fairly simple API. However, considering Rust has closures,
-//@ that should not be entirely surprising. However, as I mentioned in the beginning, Rust ensures that well-typed programs
-//@ do not have data races. How can that be? A data race is typically defined as having two concurrent, unsynchronized
+//@ The little demo above showed that concurrency in Rust has a fairly simple API. Considering Rust has closures,
+//@ that should not be entirely surprising. However, as it turns out, Rust goes well beyond this and actually ensures
+//@ the absence of data races. <br/>
+//@ A data race is typically defined as having two concurrent, unsynchronized
//@ accesses to the same memory location, at least one of which is a write. In other words, a data race is mutation in
//@ the presence of aliasing, which Rust reliably rules out! It turns out that the same mechanism that makes our single-threaded
//@ programs memory safe, and that prevents us from invalidating iterators, also helps secure our multi-threaded code against
//@ data races. For example, notice how `read_files` sends a `String` to `filter_lines`. At run-time, only the pointer to
-//@ the string will actually be moved around (just like when a `String` is passed to a function with full ownership). However,
+//@ the character data will actually be moved around (just like when a `String` is passed to a function with full ownership). However,
//@ `read_files` has to *give up* ownership of the string to perform `send`, to it is impossible for an outstanding borrow to
-//@ still be around. After it sent the string to the other side, `read_files` has no way to race on the data with someone else.
+//@ still be around. After it sent the string to the other side, `read_files` has no pointer into the string content
+//@ anymore, and hence no way to race on the data with someone else.
//@
-//@ However, there is more to this. Remember the `'static` bound we had to add to `register` in the previous part, to make
-//@ sure that the callbacks to not reference any pointers that might become invalid? This is just as crucial for spawning
+//@ There is a little more to this. Remember the `'static` bound we had to add to `register` in the previous part, to make
+//@ sure that the callbacks do not reference any pointers that might become invalid? This is just as crucial for spawning
//@ a thread: In general, that thread could last for much longer than the current stack frame. Thus, it must not use
//@ any pointers to data in that stack frame. This is achieved by requiring the `FnOnce` closure passed to `thread::spawn`
//@ to be valid for lifetime `'static`, as you can see in [its documentation](http://doc.rust-lang.org/stable/std/thread/fn.spawn.html).
//@ This avoids another kind of data race, where the thread's access races with the callee deallocating its stack frame.
+//@ It is only thanks to the concept of lifetimes that this can be expressed as part of the type of `spawn`.
//@ ## Send
-//@ However, the story goes further. I said above that `Arc` is a thread-safe version of `Rc`, which uses atomic operations
-//@ to manipulate the reference count. It is thus crucial that we don't use `Rc` above, or the reference count may become invalid.
-//@ And indeed, if you replace `Arc` by `Rc` (and add the appropriate imports), Rust will tell you that something is wrong.
-//@ That's great, of course, but how did it do that?
+//@ However, the story goes even further. I said above that `Arc` is a thread-safe version of `Rc`, which uses atomic operations
+//@ to manipulate the reference count. It is thus crucial that we don't use `Rc` across multiple threads, or the reference count may
+//@ become invalid. And indeed, if you replace `Arc` by `Rc` (and add the appropriate imports), Rust will tell you that something
+//@ is wrong. That's great, of course, but how did it do that?
//@
//@ The answer is already hinted at in the error: It will say something about `Send`. You may have noticed that the closure in
//@ `thread::spawn` does not just have a `'static` bound, but also has to satisfy `Send`. `Send` is a trait, and just like `Copy`,
-//@ it's just a marker - there are no functions provided by `Send` What the trait says is that types which are `Send`, can be
+//@ it's just a marker - there are no functions provided by `Send`. What the trait says is that types which are `Send`, can be
//@ safely sent to another thread without causing trouble. Of course, all the primitive data-types are `Send`. So is `Arc`,
//@ which is why Rust accepted our code. But `Rc` is not `Send`, and for a good reason!
//@
//@ So if the environment of your closure contains an `Rc`, it won't be `Send`, preventing it from causing trouble. If however every
//@ captured variable *is* `Send`, then so is the entire environment, and you are good.
-//@ [index](main.html) | [previous](part11.html) | [next](main.html)
+//@ [index](main.html) | [previous](part11.html) | [next](part13.html)
// Rust-101, Part 13: Slices, Arrays, External Dependencies
-// =================
+// ========================================================
//@ To complete rgrep, there are two pieces we still need to implement: Sorting, and taking the job options
//@ as argument to the program, rather than hard-coding them. Let's start with sorting.
// ## Slices
//@ Again, we first have to think about the type we want to give to our sorting function. We may be inclined to
-//@ pass it a `Vec<T>`. Now, sorting does not actually consume the argument, so we could make that a `&mut Vec<T>`.
+//@ pass it a `Vec<T>`. Of course, sorting does not actually consume the argument, so we should make that a `&mut Vec<T>`.
//@ But there's a problem with that: If we want to implement some divide-and-conquer sorting algorithm (say,
//@ Quicksort), then we will have to *split* our argument at some point, and operate recursively on the two parts.
//@ But we can't split a `Vec`! We could now extend the function signature to also take some indices, marking the
//@ part of the vector we are supposed to sort, but that's all rather clumsy. Rust offers a nicer solution.
-//@
+
//@ `[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 containing the missing
-//@ information - namely, the length. Such a pointer is called a *slice*. As we will see, a slice can be split!
+//@ 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.
pub fn sort<T: PartialOrd>(data: &mut [T]) {
if data.len() < 2 { return; }
// making sure that everything on the left is no larger than the pivot, and everything on the right is no smaller.
let mut lpos = 1;
let mut rpos = data.len();
- /* Invariant: pivot is data[0]; everything with index (0,lpos) is <= pivot; [rpos,len) is >= pivot; lpos < rpos */
+ /* 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.
+ // **Exercise 13.1**: Complete this Quicksort loop. You can use `swap` on slices to swap two elements. Write a
+ // test function for `sort`.
unimplemented!()
}
//@ 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.
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
+ //@ 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
//@ `part1`, which is the pivot. This makes sure both recursive calls work on strictly smaller slices.
sort(&mut part1[..lpos-1]); /*@*/
sort(part2); /*@*/
}
-// **Exercise 13.2*: Since `String` implements `PartialEq`, you can now change the function `output_lines` in the previous part
+// **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
// only, not by filename or line number!
//@ 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() {
- let mut data: [f64; 5] = [1.0, 3.4, 12.7, -9.12, 0.1];
- sort(&mut data);
+ let mut array_of_data: [f64; 5] = [1.0, 3.4, 12.7, -9.12, 0.1];
+ sort(&mut array_of_data);
}
// ## External Dependencies
//@ path. All of this is explained in the [Cargo Guide](http://doc.crates.io/guide.html).
// I disabled the following module (using a rather bad hack), because it only compiles if `docopt` is linked. However, before enabling it,
-// you still have get the external library into the global namespace. This is done with `extern crate docopt;`, and that statement *has* to be
-// in `main.rs`. So please go there, and enable this commented-out line. Then remove the attribute of the following module.
+// you still have get the external library into the global namespace. This is done with `extern crate docopt`, and that statement *has* to be
+// in `main.rs`. So please go there, and enable this commented-out line. Then remove the attribute of the `rgrep` module.
#[cfg(feature = "disabled")]
pub mod rgrep {
// Now that `docopt` is linked and declared in `main.rs`, we can import it with `use`. We also import some other pieces that we will need.
use part12::{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.
+ // The `USAGE` string documents how the program is to be called. It's written in a format that `docopt` can parse.
static USAGE: &'static str = "
Usage: rgrep [-c] [-s] <pattern> <file>...
// 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/).
+ // 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/).
+ //@ 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.
+ //@ There's a similar function for `Option`. `unwrap_or_else` is a bit like `unwrap`, but rather than panicking in
+ //@ case of an `Err`, it calls the closure.
let args = Docopt::new(USAGE).and_then(|d| d.parse()).unwrap_or_else(|e| e.exit());
// Now we can get all the values out.
let count = args.get_bool("-c");
}
// We need to make the strings owned to construct the `Options` instance.
- //@ If you check all the type carefully, you will notice that `pattern` above if of type `&str`. `str` is the type of a UTF-8 encoded string, that is, a bunch of
- //@ bytes in memory (`[u8]`) that are valid according of UTF-8. `str` is unsized. `&str` is a sliced string, and 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, you you cannot claim you
- //@ own them. 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`.
+ //@ If you check all the types carefully, you will notice that `pattern` above is of type `&str`. `str` is the type of a UTF-8
+ //@ 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`.
+ let mode = if count {
+ OutputMode::Count
+ } else if sort {
+ OutputMode::SortAndPrint
+ } else {
+ OutputMode::Print
+ };
Options {
files: files.iter().map(|file| file.to_string()).collect(),
pattern: pattern.to_string(),
- output_mode: if count { OutputMode::Count } else if sort { OutputMode::SortAndPrint } else { OutputMode::Print },
+ output_mode: mode,
}
}
// **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
// 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](part12.html) | [next](main.html)
c.call(0);
let mut count: usize = 0;
- c.register(Box::new(move |val| { count = count+1; println!("Callback 2, {}. time: {}", count, val); } ));
+ c.register(Box::new(move |val| {
+ count = count+1;
+ println!("Callback 2, {}. time: {}", count, val);
+ } ));
c.call(1); c.call(2);
}
}
-// Rust-101, Part 12: Concurrency (WIP)
-// =================
+// Rust-101, Part 12: Concurrency, Send
+// ====================================
use std::io::prelude::*;
use std::{io, fs, thread};
// Before we come to the actual code, we define a data-structure `Options` to store all the information we need
// to complete the job: Which files to work on, which pattern to look for, and how to output. <br/>
-// Besides just printing all the matching lines, we will also offer to count them, or alternatively to sort them.
#[derive(Clone,Copy)]
pub enum OutputMode {
Print,
}
-// The first functions reads the files, and sends every line over the `out_channel`.
+// The first function reads the files, and sends every line over the `out_channel`.
fn read_files(options: Arc<Options>, out_channel: SyncSender<String>) {
for file in options.files.iter() {
// First, we open the file, ignoring any errors.
// The second function filters the lines it receives through `in_channel` with the pattern, and sends
// matches via `out_channel`.
-fn filter_lines(options: Arc<Options>, in_channel: Receiver<String>, out_channel: SyncSender<String>) {
+fn filter_lines(options: Arc<Options>,
+ in_channel: Receiver<String>,
+ out_channel: SyncSender<String>) {
// We can simply iterate over the channel, which will stop when the channel is closed.
for line in in_channel.iter() {
// `contains` works on lots of types of patterns, but in particular, we can use it to test whether
- // one string is contained in another.
+ // one string is contained in another. This is another example of Rust using traits as substitute for overloading.
if line.contains(&options.pattern) {
unimplemented!()
}
// We move the `options` into an `Arc`, as that's what the thread workers expect.
let options = Arc::new(options);
- // Set up the channels. Use `sync_channel` with buffer-size of 16 to avoid needlessly filling RAM.
+ // This sets up the channels. We use a `sync_channel` with buffer-size of 16 to avoid needlessly filling RAM.
let (line_sender, line_receiver) = sync_channel(16);
let (filtered_sender, filtered_receiver) = sync_channel(16);
// Same with the filter thread.
let options2 = options.clone();
- let handle2 = thread::spawn(move || filter_lines(options2, line_receiver, filtered_sender));
+ let handle2 = thread::spawn(move || {
+ filter_lines(options2, line_receiver, filtered_sender)
+ });
// And the output thread.
let options3 = options.clone();
// Now we have all the pieces together for testing our rgrep with some hard-coded options.
pub fn main() {
let options = Options {
- files: vec!["src/part10.rs".to_string(), "src/part11.rs".to_string(), "src/part12.rs".to_string()],
+ files: vec!["src/part10.rs".to_string(),
+ "src/part11.rs".to_string(),
+ "src/part12.rs".to_string()],
pattern: "let".to_string(),
output_mode: Print
};
run(options);
}
-// **Exercise 12.1**: Change rgrep such that it prints now only the matching lines, but also the name of the file
+// **Exercise 12.1**: Change rgrep such that it prints not only the matching lines, but also the name of the file
// and the number of the line in the file. You will have to change the type of the channels from `String` to something
// that records this extra information.
// Rust-101, Part 13: Slices, Arrays, External Dependencies
-// =================
+// ========================================================
// ## Slices
+
pub fn sort<T: PartialOrd>(data: &mut [T]) {
if data.len() < 2 { return; }
// making sure that everything on the left is no larger than the pivot, and everything on the right is no smaller.
let mut lpos = 1;
let mut rpos = data.len();
- /* Invariant: pivot is data[0]; everything with index (0,lpos) is <= pivot; [rpos,len) is >= pivot; lpos < rpos */
+ /* 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.
+ // **Exercise 13.1**: Complete this Quicksort loop. You can use `swap` on slices to swap two elements. Write a
+ // test function for `sort`.
unimplemented!()
}
unimplemented!()
}
-// **Exercise 13.2*: Since `String` implements `PartialEq`, you can now change the function `output_lines` in the previous part
+// **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
// only, not by filename or line number!
// ## Arrays
fn sort_array() {
- let mut data: [f64; 5] = [1.0, 3.4, 12.7, -9.12, 0.1];
- sort(&mut data);
+ let mut array_of_data: [f64; 5] = [1.0, 3.4, 12.7, -9.12, 0.1];
+ sort(&mut array_of_data);
}
// ## External Dependencies
// I disabled the following module (using a rather bad hack), because it only compiles if `docopt` is linked. However, before enabling it,
-// you still have get the external library into the global namespace. This is done with `extern crate docopt;`, and that statement *has* to be
-// in `main.rs`. So please go there, and enable this commented-out line. Then remove the attribute of the following module.
+// you still have get the external library into the global namespace. This is done with `extern crate docopt`, and that statement *has* to be
+// in `main.rs`. So please go there, and enable this commented-out line. Then remove the attribute of the `rgrep` module.
#[cfg(feature = "disabled")]
pub mod rgrep {
// Now that `docopt` is linked and declared in `main.rs`, we can import it with `use`. We also import some other pieces that we will need.
use part12::{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.
+ // The `USAGE` string documents how the program is to be called. It's written in a format that `docopt` can parse.
static USAGE: &'static str = "
Usage: rgrep [-c] [-s] <pattern> <file>...
// 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/).
+ // 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/).
let args = Docopt::new(USAGE).and_then(|d| d.parse()).unwrap_or_else(|e| e.exit());
// Now we can get all the values out.
let count = args.get_bool("-c");
}
// We need to make the strings owned to construct the `Options` instance.
+ let mode = if count {
+ OutputMode::Count
+ } else if sort {
+ OutputMode::SortAndPrint
+ } else {
+ OutputMode::Print
+ };
Options {
files: files.iter().map(|file| file.to_string()).collect(),
pattern: pattern.to_string(),
- output_mode: if count { OutputMode::Count } else if sort { OutputMode::SortAndPrint } else { OutputMode::Print },
+ output_mode: mode,
}
}
// **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
// 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.)
projects / rust-101.git / commitdiff