This error occurs when an attempt is made to assign to a borrowed value.
Erroneous code example:
```compile_fail,E0506
struct FancyNum {
num: u8,
}
fn main() {
let mut fancy_num = FancyNum { num: 5 };
let fancy_ref = &fancy_num;
fancy_num = FancyNum { num: 6 };
// error: cannot assign to `fancy_num` because it is borrowed
println!("Num: {}, Ref: {}", fancy_num.num, fancy_ref.num);
}
```
Because `fancy_ref` still holds a reference to `fancy_num`, `fancy_num` can't
be assigned to a new value as it would invalidate the reference.
Alternatively, we can move out of `fancy_num` into a second `fancy_num`:
```
struct FancyNum {
num: u8,
}
fn main() {
let mut fancy_num = FancyNum { num: 5 };
let moved_num = fancy_num;
fancy_num = FancyNum { num: 6 };
println!("Num: {}, Moved num: {}", fancy_num.num, moved_num.num);
}
```
If the value has to be borrowed, try limiting the lifetime of the borrow using
a scoped block:
```
struct FancyNum {
num: u8,
}
fn main() {
let mut fancy_num = FancyNum { num: 5 };
{
let fancy_ref = &fancy_num;
println!("Ref: {}", fancy_ref.num);
}
// Works because `fancy_ref` is no longer in scope
fancy_num = FancyNum { num: 6 };
println!("Num: {}", fancy_num.num);
}
```
Or by moving the reference into a function:
```
struct FancyNum {
num: u8,
}
fn main() {
let mut fancy_num = FancyNum { num: 5 };
print_fancy_ref(&fancy_num);
// Works because function borrow has ended
fancy_num = FancyNum { num: 6 };
println!("Num: {}", fancy_num.num);
}
fn print_fancy_ref(fancy_ref: &FancyNum){
println!("Ref: {}", fancy_ref.num);
}
```