src/Logger.php
public static function getInstance(OutputInterface $output = null): ConsoleLogger
    {
        if (!isset(self::$logger)) {
            self::$logger = new ConsoleLogger($output);
        }
        return self::$logger;
    }
public static function getInstance(OutputInterface $output = null): ConsoleLogger
    {
        if (!isset(self::$logger)) {
            self::$logger = new ConsoleLogger($output);
        }
        return self::$logger;
    }
public static function getInstance ( OutputInterface $ output = null ) : ConsoleLogger { if ( ! isset ( self :: $ logger ) ) { self :: $ logger = new ConsoleLogger ( $ output ) ; } return self :: $ logger ; }
Generate or provide the single logger instance.

@param OutputInterface|null $output The output interface of symfony console. Do not be null for the first time.
@return ConsoleLogger the logger instance.
Generate or provide the single logger instance .