Trait objects

Author: BoxyUwU

src/test/ui/const-generics/defaults/trait_objects.rs

@@ -0,0 +1,45 @@
+// run-pass
+#![feature(const_generics_defaults)]
+
+trait Trait<const N: u8 = 12> {
+    fn uwu(&self) -> u8 {
+        N
+    }
+}
+
+impl Trait for u32 {}
+
+impl Trait<12> for u64 {
+    fn uwu(&self) -> u8 {
+        *self as u8
+    }
+}
+
+fn foo(arg: &dyn Trait) -> u8 {
+    arg.uwu()
+}
+
+trait Traitor<const N: u8 = 1, const M: u8 = N> {
+    fn owo(&self) -> u8 {
+        M
+    }
+}
+
+impl Traitor<2> for bool { }
+impl Traitor for u8 {
+    fn owo(&self) -> u8 {
+        *self
+    }
+}
+
+fn bar<const N: u8>(arg: &dyn Traitor<N>) -> u8 {
+    arg.owo()
+}
+
+fn main() {
+    assert_eq!(foo(&10_u32), 12);
+    assert_eq!(foo(&3_u64), 3);
+    
+    assert_eq!(bar(&true), 2);
+    assert_eq!(bar(&1_u8), 1);
+}

src/test/ui/const-generics/defaults/trait_objects_fail.rs

@@ -0,0 +1,32 @@
+#![feature(const_generics_defaults)]
+
+trait Trait<const N: u8 = 12> {
+    fn uwu(&self) -> u8 {
+        N
+    }
+}
+
+impl Trait<2> for u32 {}
+
+fn foo(arg: &dyn Trait) -> u8 {
+    arg.uwu()
+}
+
+trait Traitor<const N: u8 = 1, const M: u8 = N> {
+    fn owo(&self) -> u8 {
+        M
+    }
+}
+
+impl Traitor<2, 3> for bool { }
+
+fn bar<const N: u8>(arg: &dyn Traitor<N>) -> u8 {
+    arg.owo()
+}
+
+fn main() {
+    foo(&10_u32);
+    //~^ error: the trait bound `u32: Trait` is not satisfied
+    bar(&true);
+    //~^ error: the trait bound `bool: Traitor<{_: u8}, {_: u8}>` is not satisfied
+}

src/test/ui/const-generics/defaults/trait_objects_fail.stderr

@@ -0,0 +1,27 @@
+error[E0277]: the trait bound `u32: Trait` is not satisfied
+  --> $DIR/trait_objects_fail.rs:28:9
+   |
+LL |     foo(&10_u32);
+   |     --- ^^^^^^^ the trait `Trait` is not implemented for `u32`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the following implementations were found:
+             <u32 as Trait<2_u8>>
+   = note: required for the cast to the object type `dyn Trait`
+
+error[E0277]: the trait bound `bool: Traitor<{_: u8}, {_: u8}>` is not satisfied
+  --> $DIR/trait_objects_fail.rs:30:9
+   |
+LL |     bar(&true);
+   |     --- ^^^^^ the trait `Traitor<{_: u8}, {_: u8}>` is not implemented for `bool`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the following implementations were found:
+             <bool as Traitor<2_u8, 3_u8>>
+   = note: required for the cast to the object type `dyn Traitor<{_: u8}, {_: u8}>`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.