From: Nicola 'tekNico' Larosa Date: Sun, 21 Jan 2018 18:21:55 +0000 (+0100) Subject: part00.rs lines shortened X-Git-Url: https://git.ralfj.de/rust-101.git/commitdiff_plain/e6c369cfcd2d8ae38eb9c5cfbbee685bae2fe64d?ds=sidebyside;hp=-c part00.rs lines shortened --- e6c369cfcd2d8ae38eb9c5cfbbee685bae2fe64d diff --git a/src/part00.rs b/src/part00.rs index d126a17..eaed3d7 100644 --- a/src/part00.rs +++ b/src/part00.rs @@ -5,11 +5,12 @@ // minimum of a list. //@ ## Getting started + //@ Let us start by thinking about the *type* of our function. Rust forces us to give the types of -//@ all arguments, and the return type, before we even start writing the body. In the case of our minimum -//@ function, we may be inclined to say that it returns a number. But then we would be in trouble: What's -//@ the minimum of an empty list? The type of the function says we have to return *something*. -//@ We could just choose 0, but that would be kind of arbitrary. What we need +//@ all arguments, and the return type, before we even start writing the body. In the case of our +//@ minimum function, we may be inclined to say that it returns a number. But then we would be in +//@ trouble: What's the minimum of an empty list? The type of the function says we have to return +//@ *something*. We could just choose 0, but that would be kind of arbitrary. What we need //@ is a type that is "a number, or nothing". Such a type (of multiple exclusive options) //@ is called an "algebraic datatype", and Rust lets us define such types with the keyword `enum`. //@ Coming from C(++), you can think of such a type as a `union`, together with a field that @@ -37,22 +38,24 @@ fn vec_min(vec: Vec) -> NumberOrNothing { // Now we want to *iterate* over the list. Rust has some nice syntax for iterators: for el in vec { - // So `el` is an element of the list. We need to update `min` accordingly, but how do we get the current - // number in there? This is what pattern matching can do: + // So `el` is an element of the list. We need to update `min` accordingly, but how do we + // get the current number in there? This is what pattern matching can do: match min { - // In this case (*arm*) of the `match`, `min` is currently nothing, so let's just make it the number `el`. + // In this case (*arm*) of the `match`, `min` is currently nothing, so let's just make + // it the number `el`. NumberOrNothing::Nothing => { min = NumberOrNothing::Number(el); /*@*/ }, - // In this arm, `min` is currently the number `n`, so let's compute the new minimum and store it. + // In this arm, `min` is currently the number `n`, so let's compute the new minimum and + // store it. //@ We will write the function `min_i32` just after we completed this one. NumberOrNothing::Number(n) => { let new_min = min_i32(n, el); /*@*/ min = NumberOrNothing::Number(new_min); /*@*/ } } - //@ Notice that Rust makes sure you did not forget to handle any case in your `match`. We say - //@ that the pattern matching has to be *exhaustive*. + //@ Notice that Rust makes sure you did not forget to handle any case in your `match`. We + //@ say that the pattern matching has to be *exhaustive*. } // Finally, we return the result of the computation. return min;