Do I understand this right about yield and coroutines?

yield can only be used inside a method with IEnumerator return type. If I call another method inside this IEnumerator declared method and decide I want to start a synchronous coroutine via

yield return StartCoroutine(SomeExampleMethod());

I'm out of luck, because yield isn't allowed there.

IEnumerator A() { … }

B() { … }

IEnumerator C() { … }

A() calls B() and B() decides that it wants to start C(), but synchronous. Not possible. Instead B() needs to communicate to A() that it needs to start C().

Do I understand this correctly?

 

Yes, a function can only execute and return.

If you wanna do that, just make B() into a coroutine too.

 

I wanted to avoid that and in doing so would end up with a complicated mess.

Thanks to your answer I took a step back to looked at it again.

In the end it's an API and B() is supplied by the user. Over 99% of all cases there's no need to call C() at all. For the <1% of cases I will make it that the user supplies a coroutine and calls C() the right way.

Easy usability for over 99% of the time and a little bit tricky for the rest. Should be good UX.