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Diffstat (limited to 'compiler/rustc_error_codes/src/error_codes/E0638.md')
-rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0638.md | 47 |
1 files changed, 47 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0638.md b/compiler/rustc_error_codes/src/error_codes/E0638.md new file mode 100644 index 000000000..14cd31502 --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0638.md @@ -0,0 +1,47 @@ +This error indicates that the struct, enum or enum variant must be matched +non-exhaustively as it has been marked as `non_exhaustive`. + +When applied within a crate, downstream users of the crate will need to use the +`_` pattern when matching enums and use the `..` pattern when matching structs. +Downstream crates cannot match against non-exhaustive enum variants. + +For example, in the below example, since the enum is marked as +`non_exhaustive`, it is required that downstream crates match non-exhaustively +on it. + +```rust,ignore (pseudo-Rust) +#[non_exhaustive] +pub enum Error { + Message(String), + Other, +} + +impl Display for Error { + fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { + // This will not error, despite being marked as non_exhaustive, as this + // enum is defined within the current crate, it can be matched + // exhaustively. + let display = match self { + Message(s) => s, + Other => "other or unknown error", + }; + formatter.write_str(display) + } +} +``` + +An example of matching non-exhaustively on the above enum is provided below: + +```rust,ignore (pseudo-Rust) +use mycrate::Error; + +// This will not error as the non_exhaustive Error enum has been matched with a +// wildcard. +match error { + Message(s) => ..., + Other => ..., + _ => ..., +} +``` + +Similarly, for structs, match with `..` to avoid this error. |