Source

File: wp-includes/category.php

function get_categories( $args = '' ) {
	$defaults = array( 'taxonomy' => 'category' );
	$args     = wp_parse_args( $args, $defaults );

	/**
	 * Filters the taxonomy used to retrieve terms when calling get_categories().
	 *
	 * @since 2.7.0
	 *
	 * @param string $taxonomy Taxonomy to retrieve terms from.
	 * @param array  $args     An array of arguments. See get_terms().
	 */
	$args['taxonomy'] = apply_filters( 'get_categories_taxonomy', $args['taxonomy'], $args );

	// Back compat.
	if ( isset( $args['type'] ) && 'link' === $args['type'] ) {
		_deprecated_argument(
			__FUNCTION__,
			'3.0.0',
			sprintf(
				/* translators: 1: "type => link", 2: "taxonomy => link_category" */
				__( '%1$s is deprecated. Use %2$s instead.' ),
				'<code>type => link</code>',
				'<code>taxonomy => link_category</code>'
			)
		);
		$args['taxonomy'] = 'link_category';
	}

	$categories = get_terms( $args );

	if ( is_wp_error( $categories ) ) {
		$categories = array();
	} else {
		$categories = (array) $categories;
		foreach ( array_keys( $categories ) as $k ) {
			_make_cat_compat( $categories[ $k ] );
		}
	}

	return $categories;
}