Typed start event

[InAnYan]

LlamaIndex extensively uses typing hints for constructing workflows. In comparison to LangGraph, where you have to manually construct graph nodes and edges. LlamaIndex can do this automatically with type hints.

However, StartEvent and StopEvent are not typed. How can I restrict the type to require the StartEvent to include fields that I want?

IMHO, this feels a bit inconsistent

[dosubot[bot]]

To restrict the type of a StartEvent to include specific fields, you can create a custom subclass of StartEvent and define the fields you want using type hints. This approach allows you to enforce the presence and types of specific fields in your StartEvent. Here's an example:

from llama_index.core.workflow import StartEvent
from pydantic import BaseModel
from pathlib import Path

class MyCustomStartEvent(StartEvent):
    a_string_field: str
    a_path_to_somewhere: Path
    an_index: BaseModel  # Replace with the actual type you need
    an_llm: BaseModel    # Replace with the actual type you need

By defining a custom StartEvent like MyCustomStartEvent, you ensure that any instance of this event will include the specified fields with the required types. This method provides a consistent way to use type hints in your workflows, aligning with LlamaIndex's approach to leveraging typing for automatic workflow construction ^[1].

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[InAnYan]

I also thought about this. Will inheritance from StartEvent work? (Want an answer from maintainers)

[InAnYan]

I'm sorry.

It's written in the docs: https://docs.llamaindex.ai/en/stable/module_guides/workflow/.

I'm just confused a bit in the documentation, as there are several types of docs for different purposes