Decorators

Use Container.decorate(...) when you want explicit cross-cutting wrappers without changing consumer constructors.

DIWire keeps the current binding under an internal alias and rebinds the public key to the decorator factory. This avoids A -> Decorator(A) circular resolution errors.

Tracing Example

from typing import Protocol

from diwire import Container


class HttpClient(Protocol):
    def get(self, url: str) -> bytes: ...


class RequestsHttpClient:
    def __init__(self, base_url: str) -> None:
        self.base_url = base_url

    def get(self, url: str) -> bytes:
        return b"ok"


class Tracer:
    def span(self, name: str):
        class _Span:
            def __enter__(self) -> None:
                return None

            def __exit__(self, exc_type, exc_value, traceback) -> None:
                return None

        return _Span()


class TracedHttpClient:
    def __init__(self, inner: HttpClient, tracer: Tracer) -> None:
        self.inner = inner
        self.tracer = tracer

    def get(self, url: str) -> bytes:
        with self.tracer.span("http.get"):
            return self.inner.get(url)


container = Container()
container.add_instance("https://api.example.com", provides=str)
container.add(RequestsHttpClient, provides=HttpClient)
container.add_instance(Tracer(), provides=Tracer)
container.decorate(provides=HttpClient, decorator=TracedHttpClient)

Caching Example

class Repo:
    ...


class SqlRepo(Repo):
    ...


class CachedRepo(Repo):
    def __init__(self, inner: Repo) -> None:
        self.inner = inner


container.add(SqlRepo, provides=Repo)
container.decorate(provides=Repo, decorator=CachedRepo)

Decorator Rules

• decorate(...) can run before or after the base registration.

• Multiple decorators stack in call order: last decorate(...) call is outermost.

• Re-registering the same provides key replaces the base and rebuilds the decoration chain.

• For ambiguous inner-parameter inference, pass inner_parameter=\"<parameter_name>\" explicitly.

This is explicit provider decoration, not method interception/AOP pointcuts.