diff options
Diffstat (limited to 'compiler/rustc_error_codes/src/error_codes/E0223.md')
-rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0223.md | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0223.md b/compiler/rustc_error_codes/src/error_codes/E0223.md new file mode 100644 index 000000000..0d49f514c --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0223.md @@ -0,0 +1,33 @@ +An attempt was made to retrieve an associated type, but the type was ambiguous. + +Erroneous code example: + +```compile_fail,E0223 +trait MyTrait {type X; } + +fn main() { + let foo: MyTrait::X; +} +``` + +The problem here is that we're attempting to take the type of X from MyTrait. +Unfortunately, the type of X is not defined, because it's only made concrete in +implementations of the trait. A working version of this code might look like: + +``` +trait MyTrait {type X; } +struct MyStruct; + +impl MyTrait for MyStruct { + type X = u32; +} + +fn main() { + let foo: <MyStruct as MyTrait>::X; +} +``` + +This syntax specifies that we want the X type from MyTrait, as made concrete in +MyStruct. The reason that we cannot simply use `MyStruct::X` is that MyStruct +might implement two different traits with identically-named associated types. +This syntax allows disambiguation between the two. |