Why do I get "expected reference `&usize`" when printing?

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I have this function in Rust:

fn printboard(board: Vec<u32>) {
    println!("|  |{:>2$} {:>2$} {:>2$} {:>2$} {:>2$} {:>2$}|  |", 
        board[1], board[2], board[3], board[4], board[5], board[6]);
}

For some reason, the code throws an error at board[3], saying 'expected usize, found u32.' This does not happen with any of the other board[x] expressions. Any idea why this is happening?

Here is the full error:

error[E0308]: mismatched types
 --> src/lib.rs:3:29
  |
3 |         board[1], board[2], board[3], board[4], board[5], board[6]);
  |                             ^^^^^^^^ expected `usize`, found `u32`
  |
  = note: expected reference `&usize`
             found reference `&u32`
  = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
rust
1 Answers

If each board element should be printed with a width of 2, you should omit the $s:

fn printboard(board: Vec<u32>) {
    println!("|  |{:>2} {:>2} {:>2} {:>2} {:>2} {:>2}|  |", 
        board[1], board[2], board[3], board[4], board[5], board[6]);
}

See Width in the std::fmt docs.

The format specifier {:>2} means to align right with a width of 2, while {:>2$} means align right with a width specified by the 2nd argument (being board[3] since its 0-indexed). This width argument is required to be a usize, which is why you get the type error.

user_21891300
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