X-Git-Url: https://git.ralfj.de/rust-101.git/blobdiff_plain/fff8ebeb3f0b84c71275cbb5adee0aad6114f79b..a0ae4ec8a5da0e171cb2d2f68621fa98f5ea610b:/src/part03.rs diff --git a/src/part03.rs b/src/part03.rs index ecb8b15..b4bf2f3 100644 --- a/src/part03.rs +++ b/src/part03.rs @@ -6,7 +6,7 @@ //@ 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::*; @@ -22,45 +22,46 @@ use std::io; //@ specifying its type parameter doesn't tell us all that much. fn read_vec() -> Vec { let mut vec: Vec = Vec::::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 has type `io::Result`. //@ The problem with I/O is that it can always go wrong. The type of `line` is a lot like `Option` ("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`. + //@ 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 it's 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::` is `parse` with its generic type set to `i32`. - match line.parse::() { + match line.trim().parse::() { //@ `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) => { @@ -103,7 +104,7 @@ pub fn main() { // 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 SomethingOrNothing { @@ -115,4 +116,4 @@ impl SomethingOrNothing { // **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)