Function join 

pub fn join<'a, T>(values: &'a T, sep: &'a str) -> impl Display + 'a
where
    &'a T: IntoIterator + 'a,
    <&'a T as IntoIterator>::Item: Display + 'a,

Format a sequence, placing separator between successive elements.

Arguments

• values - The sequence of values.
• sep - The separator to insert.