Elide E0308 errors in favor of E0746
When a type error involves a `dyn Trait` as the return type, do not emit the type error, as the "return type is not `Sized`" error will provide enough information to the user.
This commit is contained in:
Esteban Küber
parent
75eabb17ae
commit
ea7e885204
6 changed files with 44 additions and 124 deletions
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@ -5,13 +5,12 @@ impl Trait for u32 {}
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fn foo() -> dyn Trait { Struct }
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//~^ ERROR E0746
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//~| ERROR E0308
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fn bar() -> dyn Trait { //~ ERROR E0746
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if true {
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return 0; //~ ERROR E0308
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return 0;
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}
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42 //~ ERROR E0308
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42
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}
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fn main() {}
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@ -1,14 +1,3 @@
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error[E0308]: mismatched types
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--> $DIR/E0746.rs:6:25
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LL | fn foo() -> dyn Trait { Struct }
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| --------- ^^^^^^ expected trait `Trait`, found struct `Struct`
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| |
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| expected `(dyn Trait + 'static)` because of return type
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= note: expected trait object `(dyn Trait + 'static)`
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found struct `Struct`
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error[E0746]: return type cannot have a bare trait because it must be `Sized`
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--> $DIR/E0746.rs:6:13
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@ -22,7 +11,7 @@ LL | fn foo() -> impl Trait { Struct }
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| ^^^^^^^^^^
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error[E0746]: return type cannot have a bare trait because it must be `Sized`
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--> $DIR/E0746.rs:10:13
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--> $DIR/E0746.rs:9:13
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LL | fn bar() -> dyn Trait {
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| ^^^^^^^^^ doesn't have a size known at compile-time
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@ -33,30 +22,5 @@ help: you can use the `impl Trait` feature in the return type because all the re
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LL | fn bar() -> impl Trait {
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| ^^^^^^^^^^
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error[E0308]: mismatched types
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--> $DIR/E0746.rs:12:16
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LL | fn bar() -> dyn Trait {
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| --------- expected `(dyn Trait + 'static)` because of return type
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LL | if true {
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LL | return 0;
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| ^ expected trait `Trait`, found integer
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= note: expected trait object `(dyn Trait + 'static)`
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found type `{integer}`
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error: aborting due to 2 previous errors
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error[E0308]: mismatched types
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--> $DIR/E0746.rs:14:5
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LL | fn bar() -> dyn Trait {
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| --------- expected `(dyn Trait + 'static)` because of return type
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...
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LL | 42
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| ^^ expected trait `Trait`, found integer
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= note: expected trait object `(dyn Trait + 'static)`
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found type `{integer}`
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error: aborting due to 5 previous errors
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For more information about this error, try `rustc --explain E0308`.
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@ -12,25 +12,23 @@ fn bar() -> (usize, dyn Trait) { (42, Struct) }
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//~| ERROR E0308
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fn bap() -> Trait { Struct }
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//~^ ERROR E0746
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//~| ERROR E0308
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fn ban() -> dyn Trait { Struct }
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//~^ ERROR E0746
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//~| ERROR E0308
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fn bak() -> dyn Trait { unimplemented!() } //~ ERROR E0277
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// Suggest using `Box<dyn Trait>`
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fn bal() -> dyn Trait { //~ ERROR E0746
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if true {
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return Struct; //~ ERROR E0308
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return Struct;
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}
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42 //~ ERROR E0308
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42
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}
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// Suggest using `impl Trait`
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fn bat() -> dyn Trait { //~ ERROR E0746
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if true {
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return 0; //~ ERROR E0308
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return 0;
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}
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42 //~ ERROR E0308
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42
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}
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fn main() {}
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@ -38,17 +38,6 @@ LL | fn bar() -> (usize, dyn Trait) { (42, Struct) }
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= note: required because it appears within the type `(usize, (dyn Trait + 'static))`
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= note: the return type of a function must have a statically known size
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:13:21
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LL | fn bap() -> Trait { Struct }
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| ----- ^^^^^^ expected trait `Trait`, found struct `Struct`
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| |
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| expected `(dyn Trait + 'static)` because of return type
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= note: expected trait object `(dyn Trait + 'static)`
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found struct `Struct`
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error[E0746]: return type cannot have a bare trait because it must be `Sized`
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:13:13
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@ -61,19 +50,8 @@ help: you can use the `impl Trait` feature in the return type because all the re
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LL | fn bap() -> impl Trait { Struct }
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| ^^^^^^^^^^
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:16:25
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LL | fn ban() -> dyn Trait { Struct }
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| --------- ^^^^^^ expected trait `Trait`, found struct `Struct`
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| |
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| expected `(dyn Trait + 'static)` because of return type
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= note: expected trait object `(dyn Trait + 'static)`
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found struct `Struct`
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error[E0746]: return type cannot have a bare trait because it must be `Sized`
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:16:13
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:15:13
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LL | fn ban() -> dyn Trait { Struct }
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| ^^^^^^^^^ doesn't have a size known at compile-time
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@ -85,7 +63,7 @@ LL | fn ban() -> impl Trait { Struct }
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| ^^^^^^^^^^
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error[E0277]: the size for values of type `(dyn Trait + 'static)` cannot be known at compilation time
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:19:13
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:17:13
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LL | fn bak() -> dyn Trait { unimplemented!() }
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| ^^^^^^^^^ doesn't have a size known at compile-time
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@ -94,26 +72,14 @@ LL | fn bak() -> dyn Trait { unimplemented!() }
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= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
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= note: the return type of a function must have a statically known size
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:23:16
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LL | fn bal() -> dyn Trait {
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| --------- expected `(dyn Trait + 'static)` because of return type
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LL | if true {
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LL | return Struct;
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| ^^^^^^ expected trait `Trait`, found struct `Struct`
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= note: expected trait object `(dyn Trait + 'static)`
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found struct `Struct`
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error[E0746]: return type cannot have a bare trait because it must be `Sized`
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:21:13
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:19:13
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LL | fn bal() -> dyn Trait {
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| ^^^^^^^^^ doesn't have a size known at compile-time
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help: if all the returned values were of the same type you could use `impl Trait` as the return type
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:25:5
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:23:5
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LL | return Struct;
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| ^^^^^^
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@ -132,20 +98,8 @@ LL | }
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LL | Box::new(42)
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:25:5
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LL | fn bal() -> dyn Trait {
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| --------- expected `(dyn Trait + 'static)` because of return type
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...
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LL | 42
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| ^^ expected trait `Trait`, found integer
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= note: expected trait object `(dyn Trait + 'static)`
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found type `{integer}`
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error[E0746]: return type cannot have a bare trait because it must be `Sized`
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:29:13
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:27:13
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LL | fn bat() -> dyn Trait {
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| ^^^^^^^^^ doesn't have a size known at compile-time
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@ -156,31 +110,7 @@ help: you can use the `impl Trait` feature in the return type because all the re
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LL | fn bat() -> impl Trait {
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| ^^^^^^^^^^
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:31:16
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LL | fn bat() -> dyn Trait {
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| --------- expected `(dyn Trait + 'static)` because of return type
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LL | if true {
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LL | return 0;
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| ^ expected trait `Trait`, found integer
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= note: expected trait object `(dyn Trait + 'static)`
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found type `{integer}`
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error[E0308]: mismatched types
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--> $DIR/dyn-trait-return-should-be-impl-trait.rs:33:5
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LL | fn bat() -> dyn Trait {
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| --------- expected `(dyn Trait + 'static)` because of return type
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...
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LL | 42
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| ^^ expected trait `Trait`, found integer
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= note: expected trait object `(dyn Trait + 'static)`
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found type `{integer}`
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error: aborting due to 15 previous errors
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error: aborting due to 9 previous errors
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Some errors have detailed explanations: E0277, E0308.
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For more information about an error, try `rustc --explain E0277`.
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