Shared &str along multiple structs conflicts with Lifetimes - rust

Question

I have the following code:
pub trait Regex: RegexClone {
fn check(&self) -> Result<u32,(/* errors should detail where it fails*/)>;
fn next(&self) -> Option<Box<dyn Regex>>;
}
pub trait RegexClone {
fn regex_clone(&self) -> Box<dyn Regex>;
}
pub struct PatternAnyCharacter<'a>{
string: &'a str
}
impl RegexClone for PatternAnyCharacter<'_> {
fn regex_clone(&self) -> Box<dyn Regex> {
return Box::new(PatternAnyCharacter {string: self.string})
}
}
impl Regex for PatternAnyCharacter<'_> {
fn check(&self) -> Result<u32, ()> {
if self.string.len() > 0 {
return Ok(1);
}
Err(())
}
fn next(&self) -> Option<Box<dyn Regex>> {
None
}
}
The idea is that when i call regex_clone i get a new Box<dyn Regex> with the same &str as member, i supossed that since im only using inmutable references when calling regex_clone it would give me a new struct with the same string slice, since is a reference im not moving anything, however the compiler complains the following:
error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
--> src/lib.rs:63:25
|
63 | return Box::new(PatternAnyCharacter {string: self.string})
| ^^^^^^^^^^^^^^^^^^^
|
note: first, the lifetime cannot outlive the lifetime `'_` as defined here...
--> src/lib.rs:61:41
|
61 | impl RegexClone for PatternAnyCharacter<'_> {
| ^^
note: ...so that reference does not outlive borrowed content
--> src/lib.rs:63:54
|
63 | return Box::new(PatternAnyCharacter {string: self.string})
| ^^^^^^^^^^^
= note: but, the lifetime must be valid for the static lifetime...
note: ...so that the types are compatible
--> src/lib.rs:63:16
|
63 | return Box::new(PatternAnyCharacter {string: self.string})
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= note: expected `Box<(dyn Regex + 'static)>`
found `Box<dyn Regex>`
How can i solve this so i can share the same string slice with multiple struct?
i thought about foregoing the string slice as member entirely and passing it as parameter to check, but hopefully i can avoid it.

Answer 1

You need to define at the trait that the returned dyn Regex can't outlive &self if you want to allow it to borrow from parts of &self.:
pub trait RegexClone {
fn regex_clone<'a>(&'a self) -> Box<dyn Regex + 'a>;
}
(You can also use an anonymous lifetime (Box<dyn Regex + '_>), but this is easier to understand.)
Side note: I don't think "clone" is the right name for such a function.