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fix: explain E0120 better cover cases when its raised

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Princess Entrapta 2024-07-19 04:15:42 +02:00
parent 8c3a94a1c7
commit af7ecb6333
1 changed files with 16 additions and 8 deletions
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24
compiler/rustc_error_codes/src/error_codes/E0120.md
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@ -1,7 +1,7 @@
Drop was implemented on a trait, which is not allowed: only structs and
enums can implement Drop.
`Drop` was implemented on a trait object or reference, which is not allowed;
only structs, enums, and unions can implement Drop.
Erroneous code example:
Erroneous code examples:
```compile_fail,E0120
trait MyTrait {}
@ -11,8 +11,16 @@ impl Drop for MyTrait {
}
```
A workaround for this problem is to wrap the trait up in a struct, and implement
Drop on that:
```compile_fail,E0120
struct Concrete {}
impl Drop for &'_ mut Concrete {
fn drop(&mut self) {}
}
```
A workaround for traits is to create a wrapper struct with a generic type,
add a trait bound to the type, and implement `Drop` on the wrapper:
```
trait MyTrait {}
@ -24,13 +32,13 @@ impl <T: MyTrait> Drop for MyWrapper<T> {
```
Alternatively, wrapping trait objects requires something:
Alternatively, the `Drop` wrapper can contain the trait object:
```
trait MyTrait {}
//or Box<MyTrait>, if you wanted an owned trait object
struct MyWrapper<'a> { foo: &'a MyTrait }
// or Box<dyn MyTrait>, if you wanted an owned trait object
struct MyWrapper<'a> { foo: &'a dyn MyTrait }
impl <'a> Drop for MyWrapper<'a> {
fn drop(&mut self) {}