Todo application

import dataclasses
import solara
from solara.lab import Ref

@dataclasses.dataclass(frozen=True)
class TodoItem:
    text: str
    done: bool

todo_item = solara.reactive(TodoItem("Buy milk", False))

# now text is a reactive variable that is always in sync with todo_item.text
text = Ref(todo_item.fields.text)


# we can now modify the reactive text variable
# and see its value reflect in the todo_item
text.value = "Buy skimmed milk"
assert todo_item.value.text == "Buy skimmed milk"

# Or, the other way around
todo_item.value = TodoItem("Buy whole milk", False)
assert text.value == "Buy whole milk"

todo_items = solara.reactive([TodoItem("Buy milk", False), TodoItem("Buy eggs", False)])
todo_item_eggs = Ref(todo_items.fields[1])
todo_item_eggs.value = TodoItem("Buy eggs", True)
assert todo_items.value[1].done == True

# However, if a list becomes shorter, and the valid index is now out of range, the
# reactive variables will act as if it is "not connected", and will not trigger
# updates anymore. Accessing the value will raise an IndexError.

todo_items.value = [TodoItem("Buy milk", False)]
# anyone listening to todo_item_eggs will *not* be notified.
try:
    value = todo_item_eggs.value
except IndexError:
    print("this is expected")
else:
    raise AssertionError("Expected an IndexError")