I’m wondering about using

apply_map

with functions that create parameters. Here’s a minimal example:

from prefect import Flow, Parameter, unmapped, apply_map

def func(x, y):
    z = Parameter('z')
    w = x + y + z
    return w

with Flow('flow') as flow:
    x = Parameter('x')
    y = Parameter('y')
    w = apply_map(func, x, y)

---------------------------------------------------------------------------
ValueError: Parameters must be root tasks and can not have upstream dependencies.

The error comes when

apply_map

tries to add edges from the root tasks of the subgraph to the argument tasks passed to

apply_map

. This fails when it tries to make an edge from

x

to

z

since

z

is a parameter. This error seems to preclude ever using

apply_map

with a function that creates a parameter. I’m wondering if that constraint is necessary. My intuition is that if

apply_map

sees a parameter that is in the subflow but not in the parent flow, it should assume that any edges from that parameter are unmapped edges that should be added to the parent flow. Does this seem right?