Sequence diagrams - support for options, alternatives, loops?

[AndreiPashkin]

UML sequence diagrams are supposed to support option, alternative and loop fragments:

But there is no explicit support for this in D2. The only way you could reflect those constructs right now is like this:

shape: sequence_diagram
# Predefine actors
alice
bob
alt: {
  condition1: {
    alice -> bob: Action 1
  }
  condition2: {
    alice -> bob: Action 2
  }
  else: {
    alice -> bob: Action 3
  }
}
opt: {
  condition4: {
    bob -> alice: Action 4
  }
}
loop: {
  condition5: {
    bob -> alice: Action 5
  }
}

Should an explicit support for these things be added?

[alixander]

I don't understand what explicit support means.

It looks like the difference between "option, alternative and loop fragments" are just the labels, and you can use any label in D2.

[terlar]

I agree for the simple case showcased here, what about alts that use several sections and have secondary labels, such as:

[terlar]

There is also dividers:

And delays:

Is it possible to achieve somehow?

[sanguineti]

I believe the best approach is for D2 to natively support all the features of a sequence diagram according to the UML standard. As @terlar evidenced above, it is not just a label.

[alixander]

@terlar Thanks for the examples. I'm convinced D2 needs something akin to the alts, delays, and dividers, as well as secondary labels like the [successful case] next to alt.

Can you provide an isolated example of loop and option being necessary?

[sanguineti]

@alixander Here are some examples