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Diffstat (limited to 'compiler/rustc_error_codes/src/error_codes/E0495.md')
-rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0495.md | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0495.md b/compiler/rustc_error_codes/src/error_codes/E0495.md new file mode 100644 index 000000000..cd10e7193 --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0495.md @@ -0,0 +1,40 @@ +#### Note: this error code is no longer emitted by the compiler. + +A lifetime cannot be determined in the given situation. + +Erroneous code example: + +```compile_fail +fn transmute_lifetime<'a, 'b, T>(t: &'a (T,)) -> &'b T { + match (&t,) { // error! + ((u,),) => u, + } +} + +let y = Box::new((42,)); +let x = transmute_lifetime(&y); +``` + +In this code, you have two ways to solve this issue: + 1. Enforce that `'a` lives at least as long as `'b`. + 2. Use the same lifetime requirement for both input and output values. + +So for the first solution, you can do it by replacing `'a` with `'a: 'b`: + +``` +fn transmute_lifetime<'a: 'b, 'b, T>(t: &'a (T,)) -> &'b T { + match (&t,) { // ok! + ((u,),) => u, + } +} +``` + +In the second you can do it by simply removing `'b` so they both use `'a`: + +``` +fn transmute_lifetime<'a, T>(t: &'a (T,)) -> &'a T { + match (&t,) { // ok! + ((u,),) => u, + } +} +``` |