The order of keys will be random and count keys with no data:

^test(1)=""
^test(10)="test"
^test(52)="hello"

The command will return 3

Out of curiosity, is there a way to do it with 'for', but i wanted to know a method for that.

I’m thinking of creating a new configuration argument, similar to "Output" itself.

Example in Java with SpringBoot. 

In this code, Spring Boot has several special variables with their own configurations. Something along those lines.

Let's think about a scenario where we need to save a user in the database. I create a method that receives a JSON with the user's information.
At this moment, I receive "name", "email", and "password". Right after that, I create a UserDTO class to map the data.
 

Method createUser(@Request user As test.UserDTO) As%Status {
	// codes...
}

The object that is arriving would be the %request.Content, and when passing it to the createUser method, our @Request is the one that deserializes the JSON into an Iris type.