/// Return Bytes setting
///
/// @access private
///
/// @param {map} $override
///   User defined settings
///
/// @param {key} $setting
///   Map key of setting
///
/// @return {boolean | color | list | number | string}
///
/// @example scss
///   $bytes: ('font-size': 14px);
///   .foo {
///     font-size: _get-setting($bytes, 'font-size');
///   }
///
/// @example css
///   .foo {
///     font-size: 16px;
///   }
@function _get-setting($override, $setting) {
  $_config: map-merge($_bytes-default, $override);

  @return unquote(map-get($_config, $setting));
}

/// Return Bytes setting
///
/// @access private
///
/// @param {map} $override
///   User defined settings
///
/// @param {key} $setting
///   Map key of setting
///
/// @return {boolean | color | list | number | string}
///
/// @example scss
///   $bytes: ('font-size': 14px);
///   .foo {
///     font-size: _get-setting($bytes, 'font-size');
///   }
///
/// @example css
///   .foo {
///     font-size: 16px;
///   }
@function _get-setting($override, $setting) {
  $_config: map-merge($_bytes-default, $override);

  @if map-get($_config, $setting) == string {
    @return unquote(map-get($_config, $setting));
  }
  
  @return map-get($_config, $setting);
}

Check if setting is a sting
Check if setting is a sting

Future versions of Sass will cause an error if a number is passed to `unquote()`