code: function concat(array, separator) {
      // TODO: Create subclass ConcatStream < Stream. Defer
      // subscribing to streams until the value() is called.
      var hasStream = scanArray(array);
      if (hasStream) {
        var stream = new ConcatStream(array, separator);
  
        for (var i = 0, l = array.length; i < l; i++) {
          addDependency(stream, array[i]);
        }
  
        return stream;
      } else {
        return array.join(separator);
      }
    }
docs: /*
  Join an array, with any streams replaced by their current values.
  
  @private
  @for Ember.stream
  @function concat
  @param {Array} array An array containing zero or more stream objects and
  zero or more non-stream objects.
  @param {String} separator String to be used to join array elements.
  @return {String} String with array elements concatenated and joined by the
  provided separator, and any stream array members having been
  replaced by the current value of the stream.