Support for ? in Day of Week and Day of Month

[dnafication]

As per the documentation of class DayOfWeekField and DayOfMonthField, it allows ? but it looks like there is no code to support the character. Due to this, following cron expression results in exception.

$cron = Cron\CronExpression::factory('0 12 * * ? *');
$cron = Cron\CronExpression::factory('0 12 ? * * *');

Error Stacktrace

Fatal error: Uncaught InvalidArgumentException: Invalid CRON field value ? at position 4 in /Users/user/aws-cron-expression/src/Cron/CronExpression.php:162
Stack trace:
#0 /Users/user/aws-cron-expression/src/Cron/CronExpression.php(143): Cron\CronExpression->setPart(4, '?')
#1 /Users/user/aws-cron-expression/src/Cron/CronExpression.php(121): Cron\CronExpression->setExpression('0 12 * * ? ')
#2 /Users/user/aws-cron-expression/src/Cron/CronExpression.php(89): Cron\CronExpression->__construct('0 12 * * ? ', Object(Cron\FieldFactory))
#3 /Users/user/aws-cron-expression/index.php(8): Cron\CronExpression::factory('0 12 * * ? ')
#4 {main}

Do you plan to implement this?

[NicoHaase]

Out of curiosity: I'm not that familiar with the meaning of the questionmark here, and I could not find a good example about when this makes a difference to the asterisk. By providing some test cases, you could help to implement this

[dnafication]

Some examples here:
https://docs.aws.amazon.com/AmazonCloudWatch/latest/events/ScheduledEvents.html#CronExpressions
https://docs.aws.amazon.com/lambda/latest/dg/services-cloudwatchevents-expressions.html

The ? (question mark) wildcard specifies one or another. In the Day-of-month field you could enter 7 and if you didn't care what day of the week the 7th was, you could enter ? in the Day-of-week field.

[dragonmantank]

The logic for if a value is valid or not is a bit dumb (there are basically two checks), and we supported ? in one check but not the other.

This is fixed in 2d923cd and will go out shortly in a bugfix release.