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:

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
    }
}