Not the OP, but I'm thinking about like closures?

Say you wanted to make a Node.js framework with callbacks that react to an event. The callback might be a closure that captured some of its surrounding variables. At that point, any of the captured variables are not trivially stack-allocated.

You might be able to do something similar to what Rust does with moving though.

Typically you would construct this state in statically allocated memory. A lot of systems work this way. Dynamic heap allocation isn’t the only alternative to stack allocation.

You could predefine your event handlers within your context, then call 'enter framework' and pass your event handlers as arguments. this is continuation passing style

it is, but more specifically it’s an eliminator for a coinductive step.

Nah we did something similar on Microsoft Band. I wrote about how - https://meanderingthoughts.hashnode.dev/cooperative-multitas...

The tldr is you had to preallocate a struct with anything you wanted captured ahead of time.

Say you wanted a map of some key to growable arrays (or maps), where the number of keys isn't known until runtime. It I understand correctly, you can't really do that because the number of growable stacks nees to be known at compile time.