Factory

This time our Greeter is a factory. Each time a Customer comes in, we make the Greeter. (Don’t worry, behind the scenes there is a cache.)

Changes

• Setup gains a greeting factory function which is registered in the registry

• This function constructs the Greeter

• It’s registered with register_factory instead of register_singleton

• That’s it…our code doesn’t know, when it asks for a Greeter, that it came from a factory instead of a singleton

Code

"""

A customer walks into a store. Do the steps to interact with them:

- Get *a* (not *the*) greeter

- Interact with them

Simple wired application:

- Registry

- Factory to get a Greeter that says hello

"""

from dataclasses import dataclass

from wired import ServiceRegistry


@dataclass
class Greeter:
    greeting: str

    def __call__(self) -> str:
        return f'{self.greeting} !!'


def setup() -> ServiceRegistry:
    # Make the registry
    registry = ServiceRegistry()

    # Make the greeter factory
    def greeter_factory(container) -> Greeter:
        return Greeter(greeting='Hello')

    # Register it as a factory using its class for the "key"
    registry.register_factory(greeter_factory, Greeter)

    return registry


def greet_a_customer(registry: ServiceRegistry) -> str:
    # A customer comes in, handle the steps in the greeting
    # as a container.
    container = registry.create_container()

    # First step in the interaction: get a greeter
    the_greeter: Greeter = container.get(Greeter)

    # Now do the steps in the interaction
    greeting = the_greeter()
    return greeting


def main():
    registry = setup()
    greeting = greet_a_customer(registry)
    assert greeting == 'Hello !!'