fn join(iter: impl IntoIterator<Item = impl ToString>) -> String {
    iter.into_iter()
        .map(|v| v.to_string())
        .collect::<Vec<_>>()
        .join(", ")
}
/// Join stringified items with ", ". Used for generating help string that lists
/// all supported fields.
Join stringified items with ", ". Used for generating help string that lists
all supported fields.
Join stringified items with " " . Used for generating help string that lists all supported fields .
fn join(iter: impl IntoIterator<Item = impl ToString>) -> String {
    iter.into_iter()
        .map(|v| v.to_string())
        .collect::<Vec<_>>()
        .join(", ")
}
fn join ( iter : impl IntoIterator < Item = impl ToString > ) -> String { iter . into_iter ( ) . map ( | v | v . to_string ( ) ) . collect :: < Vec < _ > > ( ) . join ( " " ) }
Join stringified items with ", ".
Join stringified items with " " .
iter
impl IntoIterator<Item = impl ToString>
iter
impl IntoIterator<Item = impl ToString>