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Sarj Code Standards

prefer-match-value-dispatch

Prefer match/case for repeated dispatch on one value with a fallback.

SARJ439 Rule source Tests Catalog JSON

Why

A single dispatch subject makes distinct value cases and their fallback easier to review.

Fix

Consider match/case while preserving fallback and constant semantics; use literal or dotted value patterns, never bare constant names that capture instead of compare. Review membership versus equality, subject evaluation, and guard order before rewriting.

Examples

Before — flagged Dispatch a stable parameter through literal cases
app/parse.py
def parse(kind):
    if kind == "json":
        return json_parser()
    elif kind == "yaml":
        return yaml_parser()
    else:
        return fallback()
pyproject.toml
[project]
requires-python = ">=3.10"
After — preferred Use value cases and retain the fallback
app/migrate.py
def migrate(path):
    match path.name:
        case "eslint.json":
            return rewrite_eslint(path)
        case "ratchet.json":
            return rewrite_ratchet(path)
        case _:
            return rewrite(path)
Before — flagged Keep error variants and their fallback under one dispatch subject
app/errors.py
from provider import ErrorId




def classify(error_id):
    if error_id == ErrorId.INSUFFICIENT:
        return insufficient()
    if error_id == ErrorId.INVALID_OPTION:
        return invalid_option()
    return rejected()
pyproject.toml
[project]
requires-python = ">=3.10"
After — preferred Value cases preserve the terminal fallback
app/errors.py
from provider import ErrorId




def classify(error_id):
    match error_id:
        case ErrorId.INSUFFICIENT:
            return insufficient()
        case ErrorId.INVALID_OPTION:
            return invalid_option()
        case _:
            return rejected()