[Feature Request] Workflow-init support

[cretz]

Describe the solution you'd like

Workflows need a way to run code before start to setup handlers and anything else they may want. This would accept the same input as the workflow, but can only error not return a value. Right now, especially in our languages that let you predefine handlers, it is tough to have an update/signal handler rely on workflow input.

• php Workflow-init support sdk-php#480

• typescript Workflow-init support docs sdk-typescript#1483

  • Completely unsure how to do this, maybe not worth it. But maybe we can encourage people to do file-level code.

• java Add init method to workflow sdk-java#865

  • Implementation class would have a @WorkflowInitMethod or @WorkflowConstructor or something on the constructor

• python Workflow-init support sdk-python#600

  • @workflow.init can be put on __init__ of the workflow class

• go Workflow-init support docs sdk-go#1576

  • Not needed in Go but people may like it. Can either be a register option, or maybe we can start accepting structs as workflows that must have a Run() call, but if they also have an Init() call we invoke that. Unsure, may not even be wanted

• .NET - Done

  • [WorkflowInit] already supported in this manner on .NET workflow class constructors

NOTE: This is still conceptual and subject to architectural and value discussions on whether we even want to do this much less how.

[roxblnfk]

Is it implied that tasks can be run in the init method?

[cretz]

While it technically would work, it is discouraged. I do not believe init should be async in languages that differentiate. This should just be for state. I think PHP should wait for Go and to even see where we want to do this in Go.