New upstream version 1.41.1+dfsg1

[rustc.git] / src / librustc_error_codes / error_codes / E0411.md

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+The `Self` keyword was used outside an impl, trait, or type definition.
+
+Erroneous code example:
+
+```compile_fail,E0411
+<Self>::foo; // error: use of `Self` outside of an impl, trait, or type
+             // definition
+```
+
+The `Self` keyword represents the current type, which explains why it can only
+be used inside an impl, trait, or type definition. It gives access to the
+associated items of a type:
+
+```
+trait Foo {
+    type Bar;
+}
+
+trait Baz : Foo {
+    fn bar() -> Self::Bar; // like this
+}
+```
+
+However, be careful when two types have a common associated type:
+
+```compile_fail
+trait Foo {
+    type Bar;
+}
+
+trait Foo2 {
+    type Bar;
+}
+
+trait Baz : Foo + Foo2 {
+    fn bar() -> Self::Bar;
+    // error: ambiguous associated type `Bar` in bounds of `Self`
+}
+```
+
+This problem can be solved by specifying from which trait we want to use the
+`Bar` type:
+
+```
+trait Foo {
+    type Bar;
+}
+
+trait Foo2 {
+    type Bar;
+}
+
+trait Baz : Foo + Foo2 {
+    fn bar() -> <Self as Foo>::Bar; // ok!
+}
+```