Ports¶

Ports define boundaries between components — what is expected, not how it is implemented.
They enforce architectural dependency direction at class-definition time through
__init_subclass__ validation.

Port¶

Port is the root abstract base class for the hierarchy. It uses FinalABCMeta
(which combines ABCMeta with runtime-final enforcement) and declares
__init_subclass__ as an abstract method. This forces every subclass —
InboundPort, OutboundPort, and all concrete ports — to participate in the
__init_subclass__ chain, creating the hook where dependency-direction rules
are enforced.

from forging_blocks.foundation.ports import Port

class Port(ABC, metaclass=FinalABCMeta):
    @classmethod
    @abstractmethod
    def __init_subclass__(cls, /) -> None: ...

Application code should never subclass Port directly — extend InboundPort
or OutboundPort instead.

InboundPort¶

InboundPort extends Port and marks the driving side of the hexagon:
use cases, message handlers, presenters — anything infrastructure calls into.

Its __init_subclass__ is decorated @runtime_final and runs
InboundDependencyValidator on every concrete subclass, raising
ArchitectureError if any __init__ parameter references another
InboundPort. The rule: inbound ports may only depend on outbound ports.

OutboundPort¶

OutboundPort extends Port and marks the driven side of the hexagon:
repositories, event buses, loggers, caches — anything the application core
calls out to.

Its __init_subclass__ is decorated @runtime_final and runs
OutboundDependencyValidator on every concrete subclass, raising
ArchitectureError if any __init__ parameter references an
InboundPort. The rule: outbound ports may only depend on other outbound ports.

check_methods¶

check_methods(subclass, *method_names) is a utility for
__subclasshook__ consumers. It returns True when subclass has
all the named callable attributes, enabling structural subtype checks
without explicit inheritance.

When to use¶

Extend InboundPort for protocols that define how a component is called.
Extend OutboundPort for protocols that define what a component depends on.
The __init_subclass__ validation catches architectural drift at the point
of definition — no runtime check, no CI plugin needed.