與 Rust 編譯器的鬥爭 - 6
在上一篇文章中,我們討論了與 trait 生命週期相關的編譯器錯誤。特別是,我們看到了 Box 被隱式轉換爲 Box<dyn Trait + 'static>。
在前面的例子中,我們所使用的所有特徵對象都滿足'static 生命週期,但是如果我們想要將武器特徵對象的生命週期限制放寬爲非靜態呢?
代碼如下:
trait Weapon {
fn fire(&self);
}
struct Player {
weapon: Box<dyn Weapon>,
}
impl Player {
fn new(weapon: impl Weapon + 'static) -> Self {
Self { weapon: Box::new(weapon) }
}
fn change_weapon(&mut self, weapon: impl Weapon + 'static) {
self.weapon = Box::new(weapon);
}
fn shoot(&self) {
self.weapon.fire();
}
}
struct CustomWeapon<'a> {
sound: &'a str
}
impl<'a> CustomWeapon<'a> {
fn new(sound: &'a str) -> Self {
Self { sound }
}
}
impl<'a> Weapon for CustomWeapon<'a> {
fn fire(&self) {
println!("{}", self.sound)
}
}
fn main() {
let impact = String::from("pew pew"); // non-static
let player = Player::new(CustomWeapon::new(&impact));
player.shoot(); // pew pew
}
與前面的例子不同的是,現在 CustomWeapon 有一個對非靜態對象的引用。
error[E0597]: `impact` does not live long enough
--> src/main.rs:42:48
|
41 | let impact = String::from("pew pew");
| ------ binding `impact` declared here
42 | let player = Player::new(CustomWeapon::new(&impact));
| ------------------------------^^^^^^^--
| | |
| | borrowed value does not live long enough
| argument requires that `impact` is borrowed for `'static`
43 | player.shoot(); // pew pew
44 | }
| - `impact` dropped here while still borrowed
For more information about this error, try `rustc --explain E0597`.
正如預期的那樣,編譯器抱怨 impact 對象不是靜態的。修復方法是引入生命週期泛型並替換'static,代碼修改如下:
struct Player<'a> {
weapon: Box<dyn Weapon + 'a>,
}
impl<'a> Player<'a> {
fn new(weapon: impl Weapon + 'a) -> Self {
Self { weapon: Box::new(weapon) }
}
fn change_weapon(&mut self, weapon: impl Weapon + 'a) {
self.weapon = Box::new(weapon);
}
fn shoot(&self) {
self.weapon.fire();
}
}
有了這個改變,玩家結構體不僅可以接受靜態的,也可以接受非靜態的武器特徵對象!
本文由 Readfog 進行 AMP 轉碼,版權歸原作者所有。
來源:https://mp.weixin.qq.com/s/FPpPiuheSm4bG_S2t05-cg