Rust 使用带有生命周期参数的特征作为通用边界的问题

我正在try 使用一个特征Context，它的不同实现允许Cell以不同的方式访问它的所有者World，如以下人工设计的示例代码(编译；playground here)所示:

struct Cell {    
    value: i32,    
} 
    
impl Cell {    
    fn evolve<'a>(&self, ctx: impl Context<'a>) -> Cell {    
        Cell {    
            value: self.value + ctx.get_rate()    
        }    
    }    
}    
    
struct World {    
    cell: Cell,    
    magic: i32,    
}    
    
impl World {    
    fn evolve_cell<'a, C: Context<'a>>(&'a self) -> Cell {    
        let ctx = C::new(self);        
        self.cell.evolve(ctx)        
    }    
        
    fn update(&mut self) {    
        self.cell = self.evolve_cell::<MagicContext>();    
    }    
}        
         
trait Context<'a> {    
    fn new(world: &'a World) -> Self;    
    fn get_rate(&self) -> i32;    
}    
     
struct MagicContext<'a> {    
    world: &'a World,        
}                            
                             
impl <'a> Context<'a> for MagicContext<'a> {                     
    fn new(world: &'a World) -> Self {    
        MagicContext {    
            world    
        }    
    }        
             
    fn get_rate(&self) -> i32 {    
        self.world.magic    
    }    
}        
         
fn main() {    
    let mut world = World {    
        cell: Cell { value: 2 },    
        magic: 3,    
    };    
          
    world.update();    
    println!("{}", world.cell.value);    
}

我希望能够在main中 Select 调用点的实现，而不是将MagicContext指定为World::update中的Context实现--如下所示:

impl World {    
    // ...

    fn update<C: Context>(&mut self) {    
        self.cell = self.evolve_cell::<C>();    
    }
}

// ...

fn main() {
    // ...
    world.update::<MagicContext>();
    // ...
}

但是Context需要一个生命周期参数.我不能引入像fn update<'a, C: Context<'a>>(&mut self)这样的生命周期参数，因为上下文的生命周期将阻止我Mutations self:

error[E0506]: cannot assign to `self.cell` because it is borrowed
  --> lifetime.rs:25:9
   |
24 |     fn update<'a, C: Context<'a>>(&'a mut self) {
   |               -- lifetime `'a` defined here
25 |         self.cell = self.evolve_cell::<C>();
   |         ^^^^^^^^^^^^-----------------------
   |         |           |
   |         |           borrow of `self.cell` occurs here
   |         |           argument requires that `*self` is borrowed for `'a`
   |         assignment to borrowed `self.cell` occurs here

一些看似相似的问题让我看了一下更高等级的特征界限，大约是fn update<C: for <'a> Context<'a>>(&mut self)分，但编译器告诉我:

error: implementation of `Context` is not general enough
  --> lifetime.rs:56:11
   |
56 |     world.update::<MagicContext>();
   |           ^^^^^^ implementation of `Context` is not general enough
   |
   = note: `Context<'0>` would have to be implemented for the type `MagicContext<'_>`, for any lifetime `'0`...
   = note: ...but `Context<'1>` is actually implemented for the type `MagicContext<'1>`, for some specific lifetime `'1`

我希望能够完全摆脱Context的生命周期参数，但如果没有它，我不知道如何表达new函数.

我如何才能做到这一点(或者以一种更惯用的方式实现某种类似功能)？