Question

我试图获得一些更通用的东西但是没有尝试使用相关类型。给定的是Shape特征和Renderer类型，它会尝试为特定类型的形状返回Builder。

形状

#[derive(Clone, Copy)]
pub struct Rectangle{
    pub origin: Point,
    pub height: usize,
    pub width: usize,
}

pub trait Shape{
    type Builder : ShapeBuilder;
}

impl Shape for Rectangle{
    type Builder = RectangleBuilder;
}

助洗剂

pub trait ShapeBuilder{
    type Renderer: ShapeRenderer;
    fn set_origin() -> Self::Renderer;
}

pub struct RectangleBuilder;

impl ShapeBuilder for RectangleBuilder{
    type Renderer = RectangleRenderer;
    fn set_origin() -> Self::Renderer{
        RectangleRenderer
    }
}

渲染器

pub struct Renderer<'a>{
    canvas:&'a mut Canvas
}

impl <'a>Renderer<'a>{
    pub fn new(canvas:&'a mut Canvas) -> Renderer {
        Renderer{
            canvas: canvas
        }
    }
    pub fn set_shape<T: Shape>(&self, shape: T) -> T::Builder{
        // trying to return the specific builder through shape::Builder
        // or something like that
    }
}

我想要实现的是set_shape方法会返回RectangleBuilder ，如果给定的shape类型为Rectangle

Answer 1

您需要在实例化新ShapeBuilder的{{1}}特征中提供静态方法。静态方法只是一个没有Self参数的方法。

您可以直接添加方法：

self

或聪明，并将pub trait ShapeBuilder: Sized { type Renderer: ShapeRenderer; fn new() -> Self; fn set_origin() -> Self::Renderer; }定义为Default的子广告。

ShareBuilder

然后，在pub trait ShapeBuilder: Default { type Renderer: ShapeRenderer; fn set_origin() -> Self::Renderer; }中，您可以实例化set_shape：

ShapeBuilder

通过关联类型返回泛型类型

1 个答案: