Created
July 7, 2017 17:06
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| This error code indicates a mismatch between the lifetimes appearing in the | |
| function signature (i.e., the parameter types and the return type) and the | |
| data-flow found in the function body. | |
| Erroneous code example: | |
| ```compile_fail,E0621 | |
| fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 { // explicit lifetime required | |
| // in the type of `y` | |
| if x > y { x } else { y } | |
| } | |
| ``` | |
| In the code above, the function is returning data borrowed from either `x` or `y`, | |
| but the `'a` annotation indicates that it is returning data only from `x`. To fix the | |
| error, the signature and the body must be made to match. Typically, this is done | |
| by updating the function signature. So, in this case, we change the type of `y` to | |
| `&'a i32`, like so: | |
| ``` | |
| fn foo<'a>(x: &'a i32, y: &'a i32) -> &'a i32 { | |
| if x > y { x } else { y } | |
| } | |
| ``` | |
| Now the signature indicates that the function data borrowed from either `x` or `y`. | |
| Alternatively, you could change the body not to return data from y: | |
| ``` | |
| fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 { | |
| x | |
| } | |
| ``` |
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