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Carol (Nichols || Goulding) 2016-07-21 21:51:45 -04:00
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src/ch05-00-structs.md
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@ -84,8 +84,8 @@ its argument.
## Why `struct`s? ## Why `struct`s?
Our little program is okay, but we can do better. The key is in the signature Our little program is okay, but we can do better. The key to seeing this is in
of `distance()`: the signature of `distance()`:
```rust,ignore ```rust,ignore
fn distance(x1: f64, y1: f64, x2: f64, y2: f64) -> f64 { fn distance(x1: f64, y1: f64, x2: f64, y2: f64) -> f64 {
@ -94,11 +94,11 @@ fn distance(x1: f64, y1: f64, x2: f64, y2: f64) -> f64 {
The distance function is supposed to calculate the distance between two points. The distance function is supposed to calculate the distance between two points.
But our distance function calculates some distance between four numbers. The But our distance function calculates some distance between four numbers. The
first two and last two arguments are related, but that’s not expressed anywhere first two and last two arguments are related, but that’s not expressed anywhere
in our program itself. We need a way to group `(x1, y1)` and `(x2, y2)` in our program itself. It would be nicer if we had a way to group `(x1, y1)`
together. and `(x2, y2)` together.
We’ve already discussed one way to do that: tuples. Here’s a version of our program We’ve already discussed one way to do that: tuples. Here’s a version of our
which uses tuples: program which uses tuples:
```rust ```rust
fn main() { fn main() {
@ -122,9 +122,9 @@ fn distance(p1: (f64, f64), p2: (f64, f64)) -> f64 {
``` ```
This is a little better, for sure. Tuples let us add a little bit of structure. This is a little better, for sure. Tuples let us add a little bit of structure.
We’re now passing two arguments, so that’s more clear. But it’s also worse. We’re now passing two arguments, so that’s more clear. But it’s also worse:
Tuples don’t give names to their elements, and so our calculation has gotten tuples don’t give names to their elements, so our calculation has gotten more
much more confusing: confusing:
```rust,ignore ```rust,ignore
p2.0 - p1.0 p2.0 - p1.0
@ -132,10 +132,11 @@ p2.1 - p1.1
``` ```
When writing this example, your authors almost got it wrong themselves! Distance When writing this example, your authors almost got it wrong themselves! Distance
is all about `x` and `y` points, but now it’s all about `0` and `1`. This isn’t is all about `x` and `y` points, but our code is talking about `0` and `1`.
great. This isn’t great.
Enter `struct`s. We can transform our tuples into something with a name: Enter `struct`s. We can transform our tuples into something with a name for the
whole as well as names for the parts:
```rust,ignore ```rust,ignore
let p1 = (0.0, 5.0); let p1 = (0.0, 5.0);
@ -148,7 +149,7 @@ struct Point {
let p1 = Point { x: 0.0, y: 5.0 }; let p1 = Point { x: 0.0, y: 5.0 };
``` ```
Here’s what declaring a `struct` looks like: Here’s what declaring a `struct` looks like in general:
```text ```text
struct NAME { struct NAME {