The trait std::convert::AsRef<[u8]> is not implemented for string.len() > 32

[ritiek]

If we attempt to encode a string with string.len() greater than 32, we get an error.

Modified example

extern crate qrcode;
extern crate image;

use qrcode::QrCode;
use image::Luma;

fn main() {
    // Encode some data into bits.
    let code = QrCode::new(b"this string has length 50 which is greater than 32").unwrap();

    // Render the bits into an image.
    let image = code.render::<Luma<u8>>().build();

    // Save the image.
    image.save("/tmp/qrcode.png").unwrap();
}

Here is the error

error[E0277]: the trait bound `[u8; 50]: std::convert::AsRef<[u8]>` is not satisfied
 --> src/main.rs:9:16
  |
9 |     let code = QrCode::new(b"this string has length 50 which is greater than 32").unwrap();
  |                ^^^^^^^^^^^ the trait `std::convert::AsRef<[u8]>` is not implemented for `[u8; 50]`
  |
  = help: the following implementations were found:
            <[T; <unevaluated[]>] as std::convert::AsRef<[T]>>
            <[T; <unevaluated[]>] as std::convert::AsRef<[T]>>
            <[T; <unevaluated[]>] as std::convert::AsRef<[T]>>
            <[T; <unevaluated[]>] as std::convert::AsRef<[T]>>
          and 30 others
  = note: required because of the requirements on the impl of `std::convert::AsRef<[u8]>` for `&[u8; 50]`
  = note: required by `qrcode::QrCode::new`

As it seems from std::convert::AsRef, the trait AsRef is only implemented for arrays <= 32 elements but in this case the string gets converted to byte array which happens to be > 32 elements.

[kennytm]

This is Rust's limitation (rust-lang/rust#44580) which I can't solve in this crate alone 😄. You could turn the &[u8; N] into &[u8] through this though:

    let code = QrCode::new(&b"this string has length 50 which is greater than 32"[..]).unwrap();
    //                     ^                                                     ^^^^

[ritiek]

Thanks! That seems to work.