如何为不是函数参数的引用设置生命周期？

Question

我正在尝试编译这段代码。函数 get_lines 必须生成一个 Line 的向量，将新行推送到它并 return 这个向量。

fn main() {
    let begin_point = Point{x:100, y:100};
    let end_point = Point{x:300, y:100};

    let lines = get_lines( &begin_point, &end_point);
}

fn get_lines<'a>(begin_point: &'a Point, end_point: &'a Point) -> Vec<Line<'a>>
{
    let mut lines: Vec<Line> = vec![];
    let middle_color = Color{r:0,g:0,b:0};

    let line = Line {
        begin_point: begin_point,
        end_point: end_point,
        color: &middle_color,
    };

    lines.push(line);
    lines
}

struct Color<> {r:i32, g:i32, b:i32}
struct Point {x:i32, y:i32}
struct Line<'a> {
    begin_point: &'a Point,
    end_point: &'a Point,
    color: &'a Color
}

编译失败并出现此错误：

src\main.rs:16:17: 16:29 error: `middle_color` does not live long enough
src\main.rs:16         color: &middle_color,
                               ^~~~~~~~~~~~
src\main.rs:9:1: 21:2 note: reference must be valid for the lifetime 'a as defined on the block at 9:0...
src\main.rs: 9 {
src\main.rs:10     let mut lines: Vec<Line> = vec![];
src\main.rs:11     let middle_color = Color{r:0,g:0,b:0};
src\main.rs:12
src\main.rs:13     let line = Line {
src\main.rs:14         begin_point: begin_point,
               ...
src\main.rs:11:43: 21:2 note: ...but borrowed value is only valid for the block suffix following statement 1 at 11:42
src\main.rs:11     let middle_color = Color{r:0,g:0,b:0};
src\main.rs:12
src\main.rs:13     let line = Line {
src\main.rs:14         begin_point: begin_point,
src\main.rs:15         end_point: end_point,
src\main.rs:16         color: &middle_color,
               ...
error: aborting due to previous error

如何为不是函数参数的引用设置生命周期？还是代码逻辑有问题？

Answer 1

您收到错误，因为当 get_lines() returns 时，middle_color 超出范围并被释放。如果不发生这种情况，您将在向量中得到一个悬空指针。

如果你真的想在Line中使用对color的引用，你可以在main函数中实例化它并将对它的引用传递给get_lines() ，例如：

fn get_lines<'a>(begin_point: &'a Point, end_point: &'a Point, middle_color: &'a Color) -> Vec<Line<'a>>
{
...
}

但如果这样做，您甚至可以在 main 中创建 Line 并将其移至 get_lines()。

如何为不是函数参数的引用设置生命周期？

How can I set the lifetime for a reference which isn't an argument of the function?

lifetime

rust