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Diffstat (limited to 'compiler/rustc_error_codes/src/error_codes/E0573.md')
-rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0573.md | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0573.md b/compiler/rustc_error_codes/src/error_codes/E0573.md new file mode 100644 index 000000000..6021ed0ef --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0573.md @@ -0,0 +1,71 @@ +Something other than a type has been used when one was expected. + +Erroneous code examples: + +```compile_fail,E0573 +enum Dragon { + Born, +} + +fn oblivion() -> Dragon::Born { // error! + Dragon::Born +} + +const HOBBIT: u32 = 2; +impl HOBBIT {} // error! + +enum Wizard { + Gandalf, + Saruman, +} + +trait Isengard { + fn wizard(_: Wizard::Saruman); // error! +} +``` + +In all these errors, a type was expected. For example, in the first error, if +we want to return the `Born` variant from the `Dragon` enum, we must set the +function to return the enum and not its variant: + +``` +enum Dragon { + Born, +} + +fn oblivion() -> Dragon { // ok! + Dragon::Born +} +``` + +In the second error, you can't implement something on an item, only on types. +We would need to create a new type if we wanted to do something similar: + +``` +struct Hobbit(u32); // we create a new type + +const HOBBIT: Hobbit = Hobbit(2); +impl Hobbit {} // ok! +``` + +In the third case, we tried to only expect one variant of the `Wizard` enum, +which is not possible. To make this work, we need to using pattern matching +over the `Wizard` enum: + +``` +enum Wizard { + Gandalf, + Saruman, +} + +trait Isengard { + fn wizard(w: Wizard) { // ok! + match w { + Wizard::Saruman => { + // do something + } + _ => {} // ignore everything else + } + } +} +``` |