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|
A trait implementation returns a reference without an
explicit lifetime linking it to `self`.
It commonly arises in generic trait implementations
requiring explicit lifetime bounds.
Erroneous code example:
```compile_fail,E0803
trait DataAccess<T> {
fn get_ref(&self) -> T;
}
struct Container<'a> {
value: &'a f64,
}
// Attempting to implement reference return
impl<'a> DataAccess<&f64> for Container<'a> {
fn get_ref(&self) -> &f64 { // Error: Lifetime mismatch
self.value
}
}
```
The trait method returns &f64 requiring an independent lifetime
The struct Container<'a> carries lifetime parameter 'a
The compiler cannot verify if the returned reference satisfies 'a constraints
Solution
Explicitly bind lifetimes to clarify constraints:
```
// Modified trait with explicit lifetime binding
trait DataAccess<'a, T> {
fn get_ref(&'a self) -> T;
}
struct Container<'a> {
value: &'a f64,
}
// Correct implementation (bound lifetimes)
impl<'a> DataAccess<'a, &'a f64> for Container<'a> {
fn get_ref(&'a self) -> &'a f64 {
self.value
}
}
```
|
