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Review fixes for rust-lang#32878 (which was accidentally merged)
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Manishearth committed Apr 11, 2016
1 parent 49be3dd commit 4805e12
Showing 1 changed file with 18 additions and 10 deletions.
28 changes: 18 additions & 10 deletions src/librustc_typeck/diagnostics.rs
Original file line number Diff line number Diff line change
Expand Up @@ -3645,9 +3645,8 @@ fn main() {
"##,

E0520: r##"
A non-default implementation was already made on this type
implementation so it cannot be specialized afterward. Erroneous
code example:
A non-default implementation was already made on this type so it cannot be
specialized further. Erroneous code example:
```compile_fail
#![feature(specialization)]
Expand All @@ -3656,14 +3655,18 @@ trait SpaceLama {
fn fly(&self);
}
// applies to all T
impl<T> SpaceLama for T {
default fn fly(&self) {}
}
// non-default impl
// applies to all `Clone` T and overrides the previous impl
impl<T: Clone> SpaceLama for T {
fn fly(&self) {}
}
// since `i32` is clone, this conflicts with the previous implementation
impl SpaceLama for i32 {
default fn fly(&self) {}
// error: item `fly` is provided by an `impl` that specializes
Expand All @@ -3672,28 +3675,33 @@ impl SpaceLama for i32 {
}
```
To fix this error, you need to specialize the implementation on the
parent(s) implementation first. Example:
Specialization only allows you to override `default` functions in
implementations.
```compile_fail
To fix this error, you need to mark all the parent implementations as default.
Example:
```
#![feature(specialization)]
trait SpaceLama {
fn fly(&self);
}
// applies to all T
impl<T> SpaceLama for T {
default fn fly(&self) {} // This is a parent implementation.
}
// applies to all `Clone` T; overrides the previous impl
impl<T: Clone> SpaceLama for T {
default fn fly(&self) {} // This is a parent implementation but not
// a default one so you need to add default
// keyword.
default fn fly(&self) {} // This is a parent implementation but was
// previously not a default one, causing the error
}
// applies to i32, overrides the previous two impls
impl SpaceLama for i32 {
default fn fly(&self) {} // And now that's ok!
fn fly(&self) {} // And now that's ok!
}
```
"##,
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