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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
tree | 173a775858bd501c378080a10dca74132f05bc50 /compiler/rustc_error_codes/src/error_codes/E0408.md | |
parent | Initial commit. (diff) | |
download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'compiler/rustc_error_codes/src/error_codes/E0408.md')
-rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0408.md | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0408.md b/compiler/rustc_error_codes/src/error_codes/E0408.md new file mode 100644 index 000000000..3acdbb740 --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0408.md @@ -0,0 +1,41 @@ +An "or" pattern was used where the variable bindings are not consistently bound +across patterns. + +Erroneous code example: + +```compile_fail,E0408 +match x { + Some(y) | None => { /* use y */ } // error: variable `y` from pattern #1 is + // not bound in pattern #2 + _ => () +} +``` + +Here, `y` is bound to the contents of the `Some` and can be used within the +block corresponding to the match arm. However, in case `x` is `None`, we have +not specified what `y` is, and the block will use a nonexistent variable. + +To fix this error, either split into multiple match arms: + +``` +let x = Some(1); +match x { + Some(y) => { /* use y */ } + None => { /* ... */ } +} +``` + +or, bind the variable to a field of the same type in all sub-patterns of the +or pattern: + +``` +let x = (0, 2); +match x { + (0, y) | (y, 0) => { /* use y */} + _ => {} +} +``` + +In this example, if `x` matches the pattern `(0, _)`, the second field is set +to `y`. If it matches `(_, 0)`, the first field is set to `y`; so in all +cases `y` is set to some value. |