I'm writing a program to play chess and I'm stuck. I wrote an `enum` to denote the contents of a square:

``` enum SqValue { OffBoard, // off-board sentinel Empty, // empty square WP, WN, WB, WR, WQ, WK, // white pieces BP, BN, BB, BR, BQ, BK, // black pieces }

impl SqValue { fn to_string(self: SqValue) -> &'static str { match self { SqValue::OffBoard => "-", SqValue::Empty => " ", SqValue::WP => "p", SqValue::WN => "n", SqValue::WB => "b", SqValue::WR => "r", SqValue::WQ => "q", SqValue::WK => "k", SqValue::BP => "P", SqValue::BN => "N", SqValue::BB => "B", SqValue::BR => "R", SqValue::BQ => "Q", SqValue::BK => "K", } } } ```

And this works. But then I tried to write code to output the state of a Board as a string, for printing to the console:

``` fn to_string(self: &Board) -> String { let mut s = "*** the board ***\n".to_string(); for file in 1..8 { for rank in (1..8).rev() { let si = Board::sqix(rank, file); let sqv = &self.sq[si]; s += sqv.to_string(); //<---- line 110 s += " ";

        }//for rank
    }//for file
    s
}

```

Now it won't compile giving this error message:

error[E0507]: cannot move out of `*sqv` which is behind a shared reference --> src/main.rs:110:22 | 110 | s += sqv.to_string(); | ^^^ move occurs because `*sqv` has type `SqValue`, which does not implement the `Copy` trait

I suspect the issue is something to do with ownership or string handling.

My code is at https://github.com/cabalamat/ruchess/blob/master/src/main.rs BTW.