英文:
Type-erase owner in self-referential crates
问题
我有一个结构体，并希望定义另一个引用它字段的结构体。
struct Tweet {
text: Text
}
#[ouroboros::self_referencing]
struct BorrowedText<Owner> {
owner: Arc<Owner>, // 确保在借用时不会被释放
#[borrows(owner)]
borrowed: &'this Text,
}
可以有许多类型，其中包含Text作为成员。为了防止BorrowedText<T>创建过多的类型，我想要擦除所有者类型。
#[ouroborus::self_referencing]
struct BorrowedText {
owner: Arc<dyn Any>, // 确保在借用时不会被释放
#[borrows(owner)]
borrowed: &'this Text,
}
为此，我需要从owner: Arc<Tweet>获取&Text，然后将所有者上转换为Arc<dyn Any>。我无法使用ouroborus或owning_ref API（owning_ref甚至有专用的擦除类型，如ErasedBoxRef）来使这个工作。
是否有使用ErasedBoxRef或其他API来实现这一点的方法？或者我可以安全地执行下面的操作，而无需自引用的库？
BorrowedText { owner: owner.clone(), borrowed: unsafe { (&owner.text) as (*const Text) } }
英文:
I have a struct, and want to define another struct that references its field.
struct Tweet {
text: Text
}
#[ouroboros::self_referencing]
struct BorrowedText<Owner> {
owner: Arc<Owner>, // make sure it's not deallocated while borrowing
#[borrows(owner)]
borrowed: &'this Text,
}
There can be many types that have Text as a member. To prevent BorrowedText<T> from creating too many types, I would like to erase the owner type.
#[ouroborus::self_referencing]
struct BorrowedText {
owner: Arc<dyn Any>, // make sure it's not deallocated while borrowing
#[borrows(owner)]
borrowed: &'this Text,
}
For this I need to get &Text from owner: Arc<Tweet> and then upcast owner to Arc<dyn Any>. I couldn't make this work with ouroborus or owning_ref API (owning_ref even has dedicated erased-types like ErasedBoxRef).
Is there any way to achieve this with ErasedBoxRef or other API? Or can I just safely do the below without the need for self-referential crates?
BorrowedText { owner: owner.clone(), borrowed: unsafe { (&owner.text) as (*const Text) } }
答案1
得分: 0
Manually unsafe-transmuting worked without a cost of dynamic downcast
fn f(owner: Arc<Tweet>) {
let borrowed = unsafe { std::mem::transmute::<&'_ _, &'static _>(&owner.text) };
BorrowedText {
owner: owner as Arc<dyn Send + Sync>,
borrowed,
}
}
英文:
Manually unsafe-transmuting worked without a cost of dynamic downcast
fn f(owner: Arc<Tweet>) {
let borrowed = unsafe { std::mem::transmute::<&'_ _, &'static _>(&owner.text) };
BorrowedText {
owner: owner as Arc<dyn Send + Sync>,
borrowed,
}
}
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