Document functional update syntax

Fixes #24639
This commit is contained in:
Steve Klabnik 2015-04-21 11:18:33 -04:00
parent 3860240b0e
commit f78ee1aff1

View file

@ -87,3 +87,33 @@ fn main() {
point.y = 6; // this causes an error
}
```
# Update syntax
A `struct` can include `..` to indicate that you want to use a copy of some
other struct for some of the values. For example:
```rust
struct Point3d {
x: i32,
y: i32,
z: i32,
}
let mut point = Point3d { x: 0, y: 0, z: 0 };
point = Point3d { y: 1, .. point };
```
This gives `point` a new `y`, but keeps the old `x` and `z` values. It doesnt
have to be the same `struct` either, you can use this syntax when making new
ones, and it will copy the values you dont specify:
```rust
# struct Point3d {
# x: i32,
# y: i32,
# z: i32,
# }
let origin = Point3d { x: 0, y: 0, z: 0 };
let point = Point3d { z: 1, x: 2, .. origin };
```