Side effects

Side effects are functions whose results are intentionally ignored. Side effects are dependencies themselves, so they can have their own dependencies (and even side effects ‒ though you might create a mess if go too deep).

Side effects are useful when some function should be executed before the dependency, and its result is not needed. They share the same lifespan as normal dependencies: if lifespan dependency is used as a side effect, it will be torn down after its dependant.

Side effects can be assigned globally(at function definition site) or locally(at dependant function definition site). Globally defined side effects execute every time their dependant is injected. Global side effects are additive ‒ local ones don’t override them.

Side effects are executed in a special scope that provides three values:

• “__dependant__”: the dependant’s CallableInfo

• “__values__”: a dictionary of arguments that will be passed to the dependant

• “__sccoe__”: the injection scope itself

They cannot modify the scope or the dependant since they are called after all values are resolved and ready for injection. Therefore, modifying the scope wouldn’t make much sense anyway.

Global side effect

import typing

from fundi import Scope, with_side_effects, CallableInfo, inject, scan


def side_effect(__dependant__: CallableInfo[typing.Any], __values__: dict[str, typing.Any]):
    print(__dependant__.call, "gets called with the arguments", __values__)


@with_side_effects(side_effect)
def app(a: int, b: str):
    print(a, b)


inject(Scope({"a": 1, "b": "string"}), scan(app))

Local side effect

import typing

from fundi import Scope, with_side_effects, CallableInfo, inject, scan


def side_effect(__dependant__: CallableInfo[typing.Any], __values__: dict[str, typing.Any]):
    print(__dependant__.call, "gets called with the arguments", __values__)


def app(a: int, b: str):
    print(a, b)


inject(Scope({"a": 1, "b": "string"}), scan(app, side_effects=(side_effect,)))