[英]`AsArray` cannot be made into an object when implementing a trait for a trait
Basically I'm trying to make a trait that indicates the ability to be converted into a 2D ndarray
aka ndarray::Array2
:基本上,我正在尝试制作一个特征,表明能够转换为 2D
ndarray
aka ndarray::Array2
:
trait Into2DArray{
fn to_array(&self) -> Array2<f64>;
}
I would like to do this by expanding the existingAsArray
trait, but Rust forbids me from implementing a third party trait for a third party struct ( polars::DataFrame
) for some esoteric reason, so instead I have to make my own trait for this.我想通过扩展现有的
AsArray
特征来做到这一点,但 Rust 禁止我为第三方结构( polars::DataFrame
)实现第三方特征,因为某些深奥的原因,所以我必须为此创建自己的特征.
Anyway, this works well for polars::DataFrame
:无论如何,这适用于
polars::DataFrame
:
impl Into2DArray for DataFrame {
fn to_array(&self) -> Array2<f64> {
return self.to_array();
}
}
However, I also want to implement this for anything that is already convertable into a 2D array, so I implement this trait for the AsArray
trait mentioned above:但是,我也想为任何已经可以转换为二维数组的东西实现这个,所以我为上面提到的
AsArray
特性实现了这个特性:
impl Into2DArray for AsArray<'_, f64, Ix2> {
fn to_array(&self) -> Array2<f64> {
return self.into();
}
}
However the compiler gives me grief for this:然而,编译器让我为此感到悲伤:
|
26 | impl Into2DArray for AsArray<'_, f64, Ix2> {
| ^^^^^^^^^^^^^^^^^^^^^ `AsArray` cannot be made into an object
|
= note: the trait cannot be made into an object because it requires `Self: Sized`
= note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
I understand that has something to do with object safety but I thought I had fulfilled all the criteria mentioned on that page, namely the trait doesn't return Self
, and all the generic parameters of AsArray
are specified.我知道这与对象安全有关,但我认为我已经满足了该页面上提到的所有标准,即 trait 不返回
Self
,并且指定了AsArray
所有通用参数。
What is going wrong, and how can I fix it?出了什么问题,我该如何解决?
What you were trying to do is implementing the Into2DArray
trait for the AsArray
dynamic trait object.您尝试做的是为
AsArray
动态特征对象实现Into2DArray
特征。 There should have been a warning of using AsArray
without dyn
anyway.无论如何,应该有一个警告,
AsArray
没有dyn
情况下使用AsArray
。
But this is not what you actually want.但这并不是你真正想要的。 You want to implement it for any type that implements
AsArray
.您想为任何实现
AsArray
类型实现AsArray
。 Just like you did in your comment.就像你在评论中所做的那样。
It is important to know the difference between these two things:了解这两件事之间的区别很重要:
trait NeedThis {
fn can_be_called_by_the_impl(&self) {}
}
trait ToDoThis {
fn example(&self);
}
impl ToDoThis for dyn NeedThis {
fn example(&self) {
self.can_be_called_by_the_impl()
}
}
impl NeedThis for u8 {}
fn main() {
let num: u8 = 0;
// num.example(); // doesn't work because ToDoThis is not implemented for u8
let num_as_trait_obj: &dyn NeedThis = &0_u8 as &dyn NeedThis;
num_as_trait_obj.example(); // works because this time it is a trait object
}
trait NeedThis {
fn can_be_called_by_the_impl(&self) {}
}
trait ToDoThis {
fn example(&self);
}
// removing ?Sized would make it the same as T: NeedThis + Sized
impl<T: NeedThis + ?Sized> ToDoThis for T {
fn example(&self) {
self.can_be_called_by_the_impl()
}
}
impl NeedThis for u8 {}
fn main() {
let num: u8 = 0_u8;
num.example(); // works because we implemented it for all types that implement NeedThis
let num_as_trait_obj: &dyn NeedThis = &0_u8 as &dyn NeedThis;
num_as_trait_obj.example(); // works because dyn NeedThis also implements NeedThis.
// This is only true because we added ?Sized to the bounds of the impl block.
// Otherwise it doesn't work because dyn NeedThis is not actually Sized.
// And a Sized bound is implied by default.
}
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