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Sarj Sarj Sarj Standards

prefer-required-constructor-parameters

Prefer required constructor parameters so callers choose dependencies and configuration explicitly.

SARJ468 Rule source Tests Catalog JSON

Why

Defaulted constructor parameters hide choices at the composition boundary. Replacing None with an empty string, a constant, or a factory still permits an implicit choice. A required nullable parameter makes a meaningful absent value explicit without inventing a sentinel.

Fix

Require the parameter and update callers to pass their choice explicitly; preserve meaningful None values. Suppress intentional framework or public-library defaults with a compatibility reason.

Examples

Before — flagged Constructor silently selects an empty configuration
app/service.py
class Service:
    def __init__(self, agent_name: str = "") -> None:
        self.agent_name = agent_name
After — preferred Caller explicitly chooses an absent configuration
app/service.py
class Service:
    def __init__(self, agent_name: str | None) -> None:
        self.agent_name = agent_name

Formerly: discourage-nullable-constructor-parameters