[英]Why can a function on a trait object not be called when bounded with `Self: Sized`?
[英]"this trait cannot be made into an object because it requires `Self: Sized`", except it has Sized
這是錯誤消息:
error[E0038]: the trait `room::RoomInterface` cannot be made into an object
--> src\permanent\registry\mod.rs:12:33
|
12 | pub fn load(id : String) -> Result<Box<dyn RoomInterface>, String>{
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `room::RoomInterface` cannot be made into an object
|
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>
--> src\permanent\rooms\mod.rs:36:31
|
36 | pub trait RoomInterface : Copy + Sized {
| ------------- ^^^^ ^^^^^ ...because it requires `Self: Sized`
| | |
| | ...because it requires `Self: Sized`
| this trait cannot be made into an object...
For more information about this error, try `rustc --explain E0038`.
它說要將特征用作 object,它需要 Sized。 除了 Sized 就在那里,在特性的聲明中。 它從字面上指向“Sized”這個詞並告訴我我需要“Sized”? 這是怎么回事?
問題與您的想法相反:問題是您需要Self: Sized
但只有不需要Self: Sized
的特征才能制成 object。 正如錯誤消息所述,您必須刪除RoomInterface
的Copy
和Sized
的兩個邊界:
pub trait RoomInterface {
錯誤消息中鏈接的文章是一個很好的資源,我建議閱讀它: https://doc.rust-lang.org/reference/items/traits.html#object-safety
這個討論也可能很有趣: https://users.rust-lang.org/t/trait-objects-and-the-sized-trait/14410/2
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