无法摆脱借来的内容和Builder模式

Question

我只是在学习Rust.我正在尝试为我的Game结构创建一个构建器结构.这是代码:

struct Input {
    keys_pressed: HashMap<VirtualKeyCode, bool>,
}

pub struct GameBuilder {
    settings: GameSettings,
    input: Input,
}

impl GameBuilder {
    pub fn new() -> GameBuilder {
        GameBuilder {
            settings: GameSettings {
                window_dimensions: (800, 600),
                title: "".to_string(),
            },
            input: Input {
                keys_pressed: HashMap::new(),
            }
        }
    }

    pub fn with_dimensions(&mut self, width: u32, height: u32) -> &mut GameBuilder {
        self.settings.window_dimensions = (width, height);
        self
    }

    pub fn with_title(&mut self, title: &str) -> &mut GameBuilder {
        self.settings.title = title.to_string();
        self
    }

    pub fn game_keys(&mut self, keys: Vec<VirtualKeyCode>) -> &mut GameBuilder {
        for key in keys {
            self.input.keys_pressed.insert(key, false);
        }
        self
    }

    pub fn build(&self) -> Game {
        let (width, height) = self.settings.window_dimensions;
        Game {
            display: glutin::WindowBuilder::new()
                        .with_dimensions(width, height)
                        .with_title(self.settings.title.to_string())
                        .build_glium()
                        .ok()
                        .expect("Error in WindowBuilder"),
            state: GameState::Running,
            input: self.input,
        }
    }
}

但是这段代码在最后一行抱怨input: self.input:

error: cannot move out of borrowed content

我想我理解为什么.由于在函数中传递的参数是&self,我不能取得它的所有权,以及最后一行正在做什么.

我想,也许改变&self到self会的工作,但随后编译认为我不能突变self.

还有我所知道的复制特征,也许应该可以解决问题.但是Input基本上是一个HashMap,这意味着如果散列本身太大,副本可能会很昂贵.

如何解决这个问题的好方法？

编辑:

我试过这样做:

#[derive(Debug, Copy, Clone)]
struct Input {
    keys_pressed: HashMap<VirtualKeyCode, bool>,
}

但编译器抱怨:

error: the trait `Copy` may not be implemented for this type; field `keys_pressed` does not implement `Copy`

Answer 1

鉴于您的方法签名是如何制定的,您似乎的目标是链接:

let game = GameBuilder::new().with_dimensions(...)
                             .with_title(...)
                             .build();

在Rust中,这需要GameBuilder通过值传递:

pub fn with_dimensions(self, ...) -> GameBuilder {
    // ...
}

并且为了能够self在方法中进行变异,您需要进行以下操作mut:

pub fn with_dimensions(mut self, ...) -> GameBuilder {
}

如果更改签名with_dimensions,with_title,game_keys并build采取self按值(mut self如果突变意),然后链接应该工作.