Code shared from the Rust Playground

playground.rs

use std::io::Write;

pub fn feed_type_post_body(kind: bool) -> for<'w> fn(into: &'w mut dyn Write) -> Box<dyn Write + 'w> {
    match kind {
        true => feed_rss_post_body,
        false => feed_rss_post_body,
    }
}

pub fn feed_rss_post_body<'w>(into: &'w mut dyn Write) -> Box<dyn Write + 'w> {
    Box::new(into)
}