rustyline/hint.rs
//! Hints (suggestions at the right of the prompt as you type).
/// Hints provider
pub trait Hinter {
/// Takes the currently edited `line` with the cursor `pos`ition and
/// returns the string that should be displayed or `None`
/// if no hint is available for the text the user currently typed.
fn hint(&self, line: &str, pos: usize) -> Option<String>;
}
impl Hinter for () {
fn hint(&self, _line: &str, _pos: usize) -> Option<String> {
None
}
}