Box<T> 类

Box<T> 用于分配堆内存, 并拥有这块内存的所有权.

它在标准库里的定义比较简单:

/// A pointer type that uniquely owns a heap allocation of type `T`.
pub struct Box<T: ?Sized>(Unique<T>);

Box<T> 也常用于FFI, 后面的章节会有更详细的介绍.

Box<T> 与 &T 之间的关系

Deref

函数指针

也可以用 Box<T> 来包装函数指针:

impl<Args: Tuple, F: FnOnce<Args> + ?Sized, A: Allocator> FnOnce<Args> for Box<F, A> {
    type Output = <F as FnOnce<Args>>::Output;

    extern "rust-call" fn call_once(self, args: Args) -> Self::Output {
        <F as FnOnce<Args>>::call_once(*self, args)
    }
}

impl<Args: Tuple, F: FnMut<Args> + ?Sized, A: Allocator> FnMut<Args> for Box<F, A> {
    extern "rust-call" fn call_mut(&mut self, args: Args) -> Self::Output {
        <F as FnMut<Args>>::call_mut(self, args)
    }
}

impl<Args: Tuple, F: Fn<Args> + ?Sized, A: Allocator> Fn<Args> for Box<F, A> {
    extern "rust-call" fn call(&self, args: Args) -> Self::Output {
        <F as Fn<Args>>::call(self, args)
    }
}