optionals

Optionals

Optionals are used to represent data that may or may not exist, and does so in a consistent, type safe way. This is often a convenient way to package data from sensors without extra functions involved.

Let's look at a simple sensor example

    VisionSystem vision = new Vision();
    var target = vision.getDistanceToTarget();
    if(vision.targetExists()){
        target; //do something wiwth the target data
    }
    else{
        //do something else
    }

The problem is that what if a target does not exist? What happens when you call vision.getDistanceToTarget() anyway? What should that function return when data is invalid?

One option, common in java, is to return null. Unfortunately, null is not pat of the type system, and Java will not tell you when something could be null, and when performing basically any object on a null... your code crashes. As a result, we never return a null from our functions.

So, now we have to figure out what getDistanceToTarget() should return when called on invalid data. Should it return -1? 0? Arbitrarily large value? The last valid value? What if there was no prior valid value? There's no really good answer; Any of these return schemes, can cause bugs somewhere.

Optionals provide the answer here. This is an explicit, type controlled way to say "Hey, this data may not be valid", and provides helper functions to deal with it.

public VisionSystem(){
    public Optional<double> getDistanceToTarget(){
        if(/*target exists*/) return Optional.of(1.4);
        else( Optional.empty());
    }
}

    VisionSystem vision = new Vision;

    var target = vision.getDistanceToTarget();
    if(target.isPresent()){
        target.get() //do something with the contained value
    }
    else{
        //do something else
    }

Cool! We're using optionals. While we solved the above issues, so far, we haven't gained anything in ease or convenience. Rather, we've just used the type system to prevent improper, unchecked code, and communicate this ambiguity.

But now we can deploy helper functions to simplify things based on our needs.

target.isPresent() //true if we have a target; Maybe we don't even care about the distance. 
target.isEmpty() // true if no target

double distance = vision.getDistanceToTarget().orElseGet(0) //Assume zero if no target ; No need to explicitly check if a value exists
double distance = vision.getDistanceToTarget().orElseGet(99999) //Assume big value if no target; Again, no check needed.

These extra helper functions let us assign our own defaults based on our expectations, without having to complicate the library or API.