Configuration for SpanPrinter::spacing.

This controls how much or how little whitespace is inserted into a "friendly" formatted duration. Typically, one wants less whitespace when using short unit designators (i.e., y instead of years), and more whitespace when using longer unit designators.

Example

use jiff::{
    fmt::friendly::{Designator, Spacing, SpanPrinter},
    ToSpan,
};

let span = 1.year().months(2);

// The default tries to balance spacing with compact
// unit designators.
let printer = SpanPrinter::new();
assert_eq!(printer.span_to_string(&span), "1y 2mo");

// But you can use slightly more descriptive
// designators without being too verbose.
let printer = SpanPrinter::new()
    .designator(Designator::Short);
assert_eq!(printer.span_to_string(&span), "1yr 2mos");

// When spacing is removed, it usually looks nicer
// to use compact unit designators.
let printer = SpanPrinter::new()
    .spacing(Spacing::None)
    .designator(Designator::Compact);
assert_eq!(printer.span_to_string(&span), "1y2mo");

// Conversely, when using more spacing, it usually
// looks nicer to use verbose unit designators.
let printer = SpanPrinter::new()
    .spacing(Spacing::BetweenUnitsAndDesignators)
    .designator(Designator::Verbose);
assert_eq!(printer.span_to_string(&span), "1 year 2 months");