duplicated-data

The same literal values are written out in more than one place.

Group

Code

Runs

On by default

Level

warning

Reads

Every file

Fix

None: which collection to keep, and how the others refer to it, is a design choice

Why

These collections, such as lists, map keys, or the labels a match dispatches on, hold the same values, though perhaps in another order or with a value missing. Or these functions write the same particular constant, such as a hash's prime, which usually means each carries its own copy of one algorithm. Copies must change together and drift apart when they do not. Define the values once and refer to them, or derive one collection from the other.

The fix, as Ur suggests it: define the values once and refer to them, or derive one collection from the other.

For agents

Before writing out a set of literal values or a particular constant, look for a definition that already holds them and refer to it instead.

SUPPORTED_CURRENCIES = ["USD", "EUR", "GBP", "JPY", "CHF"]

def decimals(currency):
    if currency in ("USD", "EUR", "GBP", "CHF"):
        return 2
    raise ValueError(f"unsupported currency: {currency}")

$ ur lint --rule duplicated-data
warning[duplicated-data]: 2 collections hold the same values: "USD", "EUR", "GBP", "JPY", "CHF"
  --> ./app/currencies.py:1:24 list `SUPPORTED_CURRENCIES`
  --> ./app/pricing.py:2:20 list `decimals` lacking "JPY"
  = hint: define the values once and refer to them, or derive one collection from the other
  = see: Data Clone Detection and Visualization in Spreadsheets, Felienne Hermans, Ben Sedee, Martin Pinzger, and Arie van Deursen, ICSE 2013 (2013-05), https://doi.org/10.1109/ICSE.2013.6606575
0 clone classes and 1 set of duplicated data in 2 files

Source

Data Clone Detection and Visualization in Spreadsheets, Felienne Hermans, Ben Sedee, Martin Pinzger, and Arie van Deursen, ICSE 2013 (2013-05).