Invalid warning "Possible invalid usage of ‘occurrence’"

@gallandarakhneorg , I want to follow up on error 28a:

Message: Possible invalid usage of ‘occurrence’. A impure function is detected into the sequence of calls on ‘occurrence’. Because a impure function has a possible side effect and side effect is not allowed on ‘occurrence’, it may cause an unexpected or invalid running behavior. You have to ensure by yourself that the usage of ‘occurrence’ is valid

See the code that is giving me this warning (that I want to get rid of):

on E_SetupPlayer [occurrence.agentName == this.agentName] {
		debug("Starting to register new behaviors and skills using {0} file", occurrence.configFile)

		val teamRoles = occurrence.teamRoles

and the definition of the event is just:

event E_SetupPlayer {
	var agentName : String
	var configDir : String
	var configFile : String
	var teamRoles : Map<String, Integer>
	var centralBuilder : String

	new(agentName : String, configDir : String, configFile : String, teamRoles : Map<String, Integer>, centralBuilder : String) {
		this.agentName = agentName
		this.configDir = configDir
		this.configFile = configFile
		this.teamRoles = teamRoles
		this.centralBuilder = centralBuilder
	}
}

Now why a simple assignment like:

		val teamRoles = occurrence.teamRoles

would give this warning, I am not using any (unpure) function at all. I don’t even know how one would re-write such assignment.

Thanks!

_Originally posted by @ssardina in https://github.com/sarl/sarl/issues/1010#issuecomment-646935197_

[gallandarakhneorg]

The SARL validator is now checking if the called feature is of immutable type (list of immutable types). If it is the case, no warning is generated because there is no chance to have a side-effect on the usage of occurrence.

[gallandarakhneorg]

Excellent, happy to help with “testing” and “breaking things” (the easy part…) 😉

Now, per se, occurrence.configFile is a String field in the event object and COULD be potentially changed right? The thing is that debug does not change that at all. Is this what you mean? But how does SARL know if a given function (debug here) changes or not an argument? It is a String object so it can be changed right?

A String object is immutable by definition (same as in Java). Currently, except if a SARL function is declared as @Pure, SARL assumes it is impure. But, this assumption may be wrong. That’s why the warning is make: notify the developper that a problem may exists.

Ohh is is the case that any changes to String will actualy generate a new String, not just change the referenced one? So yes any String cannot be changed per se. But this is just because it is a String, this reasoning does not apply in general.

It applies to all the types that are known to be immutable. There is a couple of them: Number, URL, UUID, etc.

So are you saying that the SARL compiler should never care about Strings passed as arguments?

Yes. Because it cannot have synchronization issue with them.