Idea of ProtocolOf is quite raw. Maybe it have to require 2nd parameter keys as (keyof Target)[]. For example:

from dataclasses import dataclass
from typing import ProtocolOf

def foo(a: int, b: float) -> float:
    return a * b


@dataclass()
class Bar:
    a: int
    b: float


FooProtocol = ProtocolOf[foo, ["__call__"]]

# (a: int, b: float) => Bar
BarNewProtocol = ProtocolOf[Bar, ["__new__"]]

(I am not a member here, so this is only my personal opinion)

This is lovely idea, I've written a similar idea recently, but as expected I was not the first to come up with an idea on this, for example you will find discussions and further links here for example:

• Add a stdlib decorator that copies/applies the ParameterSpec from one function to another cpython#107001
• https://discuss.python.org/t/extract-kwargs-types-from-a-function-signature
• Possibly there exists a topic on https://github.com/python/typing 🤔

However, typing_extensions is not the right place to discuss or introduce new ideas that still need consensus from the community. You fill find your idea better suited at the two places noted in the https://github.com/python/typing readme:

Improvements to the type system should be discussed on Python's Discourse, and are tracked in the issues in this repository.

Decide if you want to start a new discussion, or bring new input/support to the existing ones. And, hopefully we will get a concrete draft of a PEP on this to add this to the typing-specs. When more points are fledged out we can think of runtime implementations and how type-checkers have to support this.