Add bulk insert/replace capability to wpdb::insert / wpdb::replace without adding unnecessary overhead for normal single inserts

wp-db-_insert_replace_helper.php

<?php
	/**
	 * Helper function for insert and replace.
	 *
	 * Runs an insert or replace query based on $type argument.
	 *
	 * @access private
	 * @since 3.0.0
	 * @see wpdb::prepare()
	 * @see wpdb::$field_types
	 * @see wp_set_wpdb_vars()
	 *
	 * @param string $table table name
	 * @param array $data Data to insert (in column => value pairs). Both $data columns and $data values should be "raw" (neither should be SQL escaped).
	 * @param array|string $format Optional. An array of formats to be mapped to each of the value in $data. If string, that format will be used for all of the values in $data.
	 * 	A format is one of '%d', '%f', '%s' (integer, float, string). If omitted, all values in $data will be treated as strings unless otherwise specified in wpdb::$field_types.
	 * @param string $type Optional. What type of operation is this? INSERT or REPLACE. Defaults to INSERT.
	 * @return int|false The number of rows affected, or false on error.
	 */
	function _insert_replace_helper( $table, $data, $format = null, $type = 'INSERT' ) {
		if ( !in_array( strtoupper( $type ), array( 'REPLACE', 'INSERT' ) ) ) {
			return false;
		}

		$this->insert_id = 0;
		$formats = $format = (array) $format;
		$formatted_fields = array();

		// Get first value for bulk check
		$current_check = current( $data );

		// Bulk handling
		if ( is_array( $current_check ) ) {
			$fields = array_keys( $current_check );

			$rows = count( $data );

			// Handle $data like a flat array
			$data = new RecursiveIteratorIterator( new RecursiveArrayIterator( $data ) );
		}
		// Single handling
		else {
			$fields = array_keys( $data );

			$rows = 1;
		}

		foreach ( $fields as $field ) {
			if ( !empty( $format ) ) {
				$form = ( $form = array_shift( $formats ) ) ? $form : $format[ 0 ];
			}
			elseif ( isset( $this->field_types[ $field ] ) ) {
				$form = $this->field_types[ $field ];
			}
			else {
				$form = '%s';
			}

			$formatted_fields[] = $form;
		}

		$values = "(" . implode( ",", $formatted_fields ) . ")";

		// Bulk handling
		if ( 1 < $rows ) {
			$values = array_fill( 0, $rows, $values );
			$values = implode( ",", $values );
		}

		$sql = "{$type} INTO `$table` (`" . implode( '`,`', $fields ) . "`) VALUES " . $values;

		return $this->query( $this->prepare( $sql, $data ) );
	}