function setToPairs(set) {
    var index = -1,
        result = Array(set.size);

    set.forEach(function(value) {
      result[++index] = [value, value];
    });
    return result;
  }
Converts `set` to its value-value pairs.

@private
@param {Object} set The set to convert.
@returns {Array} Returns the value-value pairs.