Rust errors / Types and traits
Rust compiler error · checked with rustc 1.99.0
Rust error E0366: `Drop` impls cannot be specialized
What it meansAn attempt was made to implement Drop on a concrete specialization of a generic type. An example is shown below:
What rustc prints
error[E0366]: `Drop` impls cannot be specialized --> main.rs:5:1 | 5 | impl Drop for Foo<u32> { | ^^^^^^^^^^^^^^^^^^^^^^ | = note: `u32` is not a generic parameter note: use the same sequence of generic lifetime, type and const parameters as the struct definition --> main.rs:1:1 | 1 | struct Foo<T> { | ^^^^^^^^^^^^^
Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.
The compiler team's explanation
An attempt was made to implement Drop on a concrete specialization of a generic type. An example is shown below:
struct Foo<T> {
t: T
}
impl Drop for Foo<u32> {
fn drop(&mut self) {}
}This code is not legal: it is not possible to specialize Drop to a subset of implementations of a generic type. One workaround for this is to wrap the generic type, as shown below:
struct Foo<T> {
t: T
}
struct Bar {
t: Foo<u32>
}
impl Drop for Bar {
fn drop(&mut self) {}
}From rustc --explain E0366 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.
Related errors
- E0308mismatched types
- E0277the trait bound is not satisfied
- E0599no method named X found in the current scope
- E0433failed to resolve
- E0328explicit impls for the `Unsize` trait are not permitted
- E0364`foo` is private, and cannot be re-exported
- E0367`Drop` impl requires `T: Foo` but the struct it is implemented for does not
- E0368binary assignment operation `<<=` cannot be applied to type `f32`
Up next
Often hit nextE0308: mismatched typesA related error from the same family.Read it next →Did this answer your question?