//@ I/O is a complicated topic, so the code to do that is not exactly pretty - but well,
//@ let's get that behind us.
-// I/O is provided by the module `std::io`, so we first have import that with `use`.
+// I/O is provided by the module `std::io`, so we first have to import that with `use`.
// We also import the I/O *prelude*, which makes a bunch of commonly used I/O stuff
// directly available.
use std::io::prelude::*;
//@ specifying its type parameter doesn't tell us all that much.
fn read_vec() -> Vec<i32> {
let mut vec: Vec<i32> = Vec::<i32>::new();
- // The central handle to the standard input is made available by `io::stdin()`.
+ // The central handle to the standard input is made available by the function `io::stdin`.
let stdin = io::stdin();
- println!("Enter a list of numbers, one per line. End with Ctrl-D.");
+ println!("Enter a list of numbers, one per line. End with Ctrl-D (Linux) or Ctrl-Z (Windows).");
//@ We would now like to iterate over standard input line-by-line. We can use a `for` loop
//@ for that, but there is a catch: What happens if there is some other piece of code running
//@ concurrently, that also reads from standard input? The result would be a mess. Hence
- //@ Rust requires us to `lock()` standard input if we want to perform large operations on
- //@ it. (See [the documentation](http://doc.rust-lang.org/stable/std/io/struct.Stdin.html) for more
+ //@ Rust requires us to `lock` standard input if we want to perform large operations on
+ //@ it. (See [the documentation](https://doc.rust-lang.org/stable/std/io/struct.Stdin.html) for more
//@ details.)
for line in stdin.lock().lines() {
// Rust's type for (dynamic, growable) strings is `String`. However, our variable `line`
- // here is not yet of that type: It rather has type `io::Result<String>`.
- //@ The problem with I/O is that it can always go wrong. The type of `line`is a lot like `Option<String>` ("a `String` or
+ // here is not yet of that type: It has type `io::Result<String>`.
+ //@ The problem with I/O is that it can always go wrong. The type of `line` is a lot like `Option<String>` ("a `String` or
//@ nothing"), but in the case of "nothing", there is additional information about the error.
- //@ Again, I recommend to check [the documentation](http://doc.rust-lang.org/stable/std/io/type.Result.html).
+ //@ Again, I recommend to check [the documentation](https://doc.rust-lang.org/stable/std/io/type.Result.html).
//@ You will see that `io::Result` is actually just an alias for `Result`, so click on that to obtain
//@ the list of all constructors and methods of the type.
- //@ We will be lazy here and just assume that nothing goes wrong: `unwrap()` returns the `String` if there is one,
+ //@ We will be lazy here and just assume that nothing goes wrong: `unwrap` returns the `String` if there is one,
//@ and panics the program otherwise. Since a `Result` carries some details about the error that occurred,
//@ there will be a somewhat reasonable error message. Still, you would not want a user to see such
//@ an error, so in a "real" program, we would have to do proper error handling.
- //@ Can you find the documentation of `Result::unwrap()`?
+ //@ Can you find the documentation of `Result::unwrap`?
//@
// I chose the same name (`line`) for the new variable to ensure that I will never, accidentally,
// access the "old" `line` again.
let line = line.unwrap();
// Now that we have our `String`, we want to make it an `i32`.
- //@ `parse` is a method on `String` that can convert a string to anything. Try finding it's documentation!
+ //@ We first `trim` the `line` to remove leading and trailing whitespace.
+ //@ `parse` is a method on `String` that can convert a string to anything. Try finding its documentation!
//@ In this case, Rust *could* figure out automatically that we need an `i32` (because of the return type
//@ of the function), but that's a bit too much magic for my taste. We are being more explicit here:
//@ `parse::<i32>` is `parse` with its generic type set to `i32`.
- match line.parse::<i32>() {
+ match line.trim().parse::<i32>() {
//@ `parse` returns again a `Result`, and this time we use a `match` to handle errors (like, the user entering
//@ something that is not a number).
//@ This is a common pattern in Rust: Operations that could go wrong will return `Option` or `Result`.
//@ The only way to get to the value we are interested in is through pattern matching (and through helper functions
- //@ like `unwrap()`). If we call a function that returns a `Result`, and throw the return value away,
+ //@ like `unwrap`). If we call a function that returns a `Result`, and throw the return value away,
//@ the compiler will emit a warning. It is hence impossible for us to *forget* handling an error,
//@ or to accidentally use a value that doesn't make any sense because there was an error producing it.
Ok(num) => {
// Notice that I called the function on `SomethingOrNothing` `print2` to disambiguate from the `print` defined previously.
//
// *Hint*: There is a macro `print!` for printing without appending a newline.
-trait Print {
+pub trait Print {
/* Add things here */
}
impl<T: Print> SomethingOrNothing<T> {
// **Exercise 03.2**: Building on exercise 02.2, implement all the things you need on `f32` to make your
// program work with floating-point numbers.
-//@ [index](main.html) | [previous](part02.html) | [next](part04.html)
+//@ [index](main.html) | [previous](part02.html) | [raw source](workspace/src/part03.rs) | [next](part04.html)
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