get_option( string $option, mixed $default_value = false )

function get_option( $option, $default = false ) {
	global $wpdb;

	$option = trim( $option );
	if ( empty( $option ) )
		return false;

	/**
	 * Filters the value of an existing option before it is retrieved.
	 *
	 * The dynamic portion of the hook name, `$option`, refers to the option name.
	 *
	 * Passing a truthy value to the filter will short-circuit retrieving
	 * the option value, returning the passed value instead.
	 *
	 * @since WP-1.5.0
	 * @since WP-4.4.0 The `$option` parameter was added.
	 * @since WP-4.9.0 The `$default` parameter was added.
	 *
	 *
	 * @param bool|mixed $pre_option The value to return instead of the option value. This differs from
	 *                               `$default`, which is used as the fallback value in the event the option
	 *                               doesn't exist elsewhere in get_option(). Default false (to skip past the
	 *                               short-circuit).
	 * @param string     $option     Option name.
	 * @param mixed      $default    The fallback value to return if the option does not exist.
	 *                               Default is false.
	 */
	$pre = apply_filters( "pre_option_{$option}", false, $option, $default );

	if ( false !== $pre )
		return $pre;

	if ( defined( 'WP_SETUP_CONFIG' ) )
		return false;

	// Distinguish between `false` as a default, and not passing one.
	$passed_default = func_num_args() > 1;

	if ( ! wp_installing() ) {
		// prevent non-existent options from triggering multiple queries
		$notoptions = wp_cache_get( 'notoptions', 'options' );
		if ( isset( $notoptions[ $option ] ) ) {
			/**
			 * Filters the default value for an option.
			 *
			 * The dynamic portion of the hook name, `$option`, refers to the option name.
			 *
			 * @since WP-3.4.0
			 * @since WP-4.4.0 The `$option` parameter was added.
			 * @since WP-4.7.0 The `$passed_default` parameter was added to distinguish between a `false` value and the default parameter value.
			 *
			 * @param mixed  $default The default value to return if the option does not exist
			 *                        in the database.
			 * @param string $option  Option name.
			 * @param bool   $passed_default Was `get_option()` passed a default value?
			 */
			return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
		}

		$alloptions = wp_load_alloptions();

		if ( isset( $alloptions[$option] ) ) {
			$value = $alloptions[$option];
		} else {
			$value = wp_cache_get( $option, 'options' );

			if ( false === $value ) {
				$row = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );

				// Has to be get_row instead of get_var because of funkiness with 0, false, null values
				if ( is_object( $row ) ) {
					$value = $row->option_value;
					wp_cache_add( $option, $value, 'options' );
				} else { // option does not exist, so we must cache its non-existence
					if ( ! is_array( $notoptions ) ) {
						 $notoptions = array();
					}
					$notoptions[$option] = true;
					wp_cache_set( 'notoptions', $notoptions, 'options' );

					/** This filter is documented in wp-includes/option.php */
					return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
				}
			}
		}
	} else {
		$suppress = $wpdb->suppress_errors();
		$row = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );
		$wpdb->suppress_errors( $suppress );
		if ( is_object( $row ) ) {
			$value = $row->option_value;
		} else {
			/** This filter is documented in wp-includes/option.php */
			return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
		}
	}

	// If home is not set use siteurl.
	if ( 'home' == $option && '' == $value )
		return get_option( 'siteurl' );

	if ( in_array( $option, array('siteurl', 'home', 'category_base', 'tag_base') ) )
		$value = untrailingslashit( $value );

	/**
	 * Filters the value of an existing option.
	 *
	 * The dynamic portion of the hook name, `$option`, refers to the option name.
	 *
	 * @since WP-1.5.0 As 'option_' . $setting
	 * @since WP-3.0.0
	 * @since WP-4.4.0 The `$option` parameter was added.
	 *
	 * @param mixed  $value  Value of the option. If stored serialized, it will be
	 *                       unserialized prior to being returned.
	 * @param string $option Option name.
	 */
	return apply_filters( "option_{$option}", maybe_unserialize( $value ), $option );
}