/// Converts shorthand to the 4-value syntax.
///
/// @param {List} $shorthand
///
/// @example scss - Usage
///   .element {
///     margin: unpack(1em 2em);
///   }
///
/// @example css - CSS Output
///   .element {
///     margin: 1em 2em 1em 2em;
///   }

@function unpack($shorthand) {
  @if $output-bourbon-deprecation-warnings == true {
    @warn "[Bourbon] [Deprecation] `unpack` is deprecated and will be " +
    "removed in 5.0.0.";
  }

  @if length($shorthand) == 1 {
    @return nth($shorthand, 1) nth($shorthand, 1) nth($shorthand, 1) nth($shorthand, 1);
  } @else if length($shorthand) == 2 {
    @return nth($shorthand, 1) nth($shorthand, 2) nth($shorthand, 1) nth($shorthand, 2);
  } @else if length($shorthand) == 3 {
    @return nth($shorthand, 1) nth($shorthand, 2) nth($shorthand, 3) nth($shorthand, 2);
  } @else {
    @return $shorthand;
  }
}