Function display_utils::join_format

pub fn join_format<I, J, C>(
    iterator: I, 
    joiner: J, 
    callback: C
) -> JoinFormat<I::IntoIter, J, C> where
    I: IntoIterator,
    I::IntoIter: Clone,
    J: Display,
    C: Fn(I::Item, &mut Formatter<'_>) -> Result, 

Concatenate iterator elements, separating each element pair with a given joiner, where each iterator element can be formatted using a callback.

The callback must be Fn and the iterator must be cloneable, because Display objects may be printed multiple times.

let strings = &["hello", "wonderful", "world"];

let output = join_format(
    strings.iter().enumerate(),
    ", ",
    |(i, string), f| write!(f, "{}={}", i, string),
);
assert_eq!(output.to_string(), "0=hello, 1=wonderful, 2=world");