CODEWITHSUNDEEP
referencerustlifetime
jeremiah
jeremiah

Reputation: 81

the lifetime 'a as defined on the body does not necessarily outlive the anonymous lifetime #1 defined on the body

I'm trying to create a function (f1) that adds an element to an array.

Here is my Rust code:

use std::mem;

struct T1<'a> {
    value: &'a str,
}

fn main() {   
    let mut data: [T1; 1] = unsafe { mem::uninitialized() };
    f1("Hello", &mut data[..]);
}

fn f1<'b, 'a: 'b>(s: &'a str, data: &'b mut[T1]) {   
    data[0] = T1::<'a> { value: s };
}

I get this error message:

error[E0308]: mismatched types
  --> <anon>:13:15
   |
13 |     data[0] = T1::<'a> { value: s };
   |               ^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
   |
   = note: expected type `T1<'_>`
   = note:    found type `T1<'a>`
note: the lifetime 'a as defined on the body at 12:49...
  --> <anon>:12:50
   |
12 |   fn f1<'b, 'a: 'b>(s: &'a str, data: &'b mut[T1]) {   
   |  __________________________________________________^ starting here...
13 | |     data[0] = T1::<'a> { value: s };
14 | | }
   | |_^ ...ending here
note: ...does not necessarily outlive the anonymous lifetime #1 defined on the body at 12:49
  --> <anon>:12:50
   |
12 |   fn f1<'b, 'a: 'b>(s: &'a str, data: &'b mut[T1]) {   
   |  __________________________________________________^ starting here...
13 | |     data[0] = T1::<'a> { value: s };
14 | | }
   | |_^ ...ending here
help: consider using an explicit lifetime parameter as shown: fn f1<'b, 'a:'b>(s: &'a str, data: &'b mut [T1<'a>])
  --> <anon>:12:1
   |
12 |   fn f1<'b, 'a: 'b>(s: &'a str, data: &'b mut[T1]) {   
   |  _^ starting here...
13 | |     data[0] = T1::<'a> { value: s };
14 | | }
   | |_^ ...ending here

Is there a way to write f1 that does what I'm trying to do?

Upvotes: 3

Views: 3150

Answers (1)

Ankur
Ankur

Reputation: 33657

You need to specify lifetime to the slice parameter:

fn f1<'b, 'a: 'b>(s: &'a str, data: &'b mut [T1<'a>]) {
    data[0] = T1::<'a> { value: s };
}

Upvotes: 1

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