Singletons Example

In this example you’ll see how we define dependencies as singletons and how they behave.

A singleton injectable is instantiated only once and then this same instance is used whenever an injection is made.

In our Singleton example class we inject two parameters, client1 and client2 both with the SingletonClient class, which in turn, was declared as singleton.

When we run our example we can see that, as there is only one instance being shared between injections a change to its state is then reflected to every other place injected with it.

singleton_example.py

from examples import Example
from examples.singletons.singleton_client import SingletonClient
from injectable import Autowired, autowired, load_injection_container


class Singletons(Example):
    @autowired
    def __init__(
        self,
        client1: Autowired(SingletonClient),
        client2: Autowired(SingletonClient),
    ):
        self.client1 = client1
        self.client2 = client2

    def run(self):
        print(self.client1.connected)
        # False

        print(self.client2.connected)
        # False

        self.client1.connect()
        print(self.client1.connected)
        # True

        print(self.client2.connected)
        # True


def run_example():
    load_injection_container()
    example = Singletons()
    example.run()


if __name__ == "__main__":
    run_example()

singleton_client.py

from injectable import injectable


@injectable(singleton=True)
class SingletonClient:
    def __init__(self):
        self.connected = False

    def connect(self):
        self.connected = True