Chapter 4 Downcast

The following example shows how you can downcast a Box<dyn AudioTag> into its “backend” tag type. This allows you to set the uncommon metadata supported by the corresponding backend but not by audiotags.

use audiotags::*;

fn main() {
    let mut innertag = metaflac::Tag::default();
    innertag
        .vorbis_comments_mut()
        .set_title(vec!["title from metaflac::Tag"]);
    let tag: FlacTag = innertag.into();
    let mut id3tag = tag.to_dyn_tag(TagType::Id3v2);
    id3tag
        .write_to_path("assets/a.mp3")
        .expect("Fail to write!");

    let id3tag_reload = Tag::default()
        .read_from_path("assets/a.mp3")
        .expect("Fail to read!");
    assert_eq!(id3tag_reload.title(), Some("title from metaflac::Tag"));

    let mut id3tag_inner: id3::Tag = id3tag_reload.try_into().unwrap();
    // this would fail if `id3tag_reload` isn't really a id3 tag.

    let timestamp = id3::Timestamp {
        year: 2013,
        month: Some(2u8),
        day: Some(5u8),
        hour: Some(6u8),
        minute: None,
        second: None,
    };
    id3tag_inner.set_date_recorded(timestamp.clone());
    id3tag_inner
        .write_to_path("assets/a.mp3", id3::Version::Id3v24)
        .expect("Fail to write!");

    let id3tag_reload = id3::Tag::read_from_path("assets/a.mp3")
        .expect("Fail to read!");
    assert_eq!(id3tag_reload.date_recorded(), Some(timestamp));
}