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[[Rust]]
[[Data must outlive any references to it]]
Associated permission: Flow:
Indicates whether or not a reference argument is allowed to be used, or a reference is allowed to be returned.
Simple example:
```rust
fn a_or_b(a: &str, b: &str) -> &str {
if something {
a
} else {
b
}
}
let a = vec![];
let b = String::from("a");
let c = a_or_b(&a, &b);
drop(b);
println!("{}", c);
```
In the above example `c` is being printed after `b` is dropped but `a_or_b` could have returned `b` so the println uses freed data ( null pointer exception) .
It is also not possible to return a reference to heap data that will be dropped at the end of the function.
```rust
fn epic_ref() -> &str {
let cool = String::from("yo");
let coolref = &cool;
coolref
}
```
^ will fail
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