Credence.Pattern.NoMapKeysOrValuesForIteration (credence v0.4.1)

Performance rule: Detects Map.values(map) or Map.keys(map) passed directly into an Enum function, which creates an unnecessary intermediate list.

All Enum functions accept maps directly and iterate over {key, value} pairs without allocating an intermediate list.

Automatic fixing

# Callback wrapping
Enum.all?(Map.values(degrees), fn v -> v == 0 end)
→ Enum.all?(degrees, fn {_k, v} -> v == 0 end)

# max/min → max_by/min_by + elem
Enum.max(Map.values(m))
→ Enum.max_by(m, fn {_k, v} -> v end) |> elem(1)

# sum/product → reduce
Enum.sum(Map.values(m))
→ Enum.reduce(m, 0, fn {_k, v}, acc -> acc + v end)

# find/at → case expression
Enum.find(Map.values(m), fn v -> v > 0 end)
→ case Enum.find(m, fn {_k, v} -> v > 0 end) do
    nil -> nil; {_, v} -> v
  end

# filter/sort/etc → chain with Enum.map
Map.keys(m) |> Enum.filter(fn k -> k > 0 end)
→ m |> Enum.filter(fn {k, _v} -> k > 0 end)
  |> Enum.map(fn {k, _v} -> k end)

Functions returning complex structures (chunk_every, zip, split, with_index, scan, tally, etc.) cannot be safely auto-fixed and are handled by NoMapKeysOrValuesForRawIteration.

Bad

Enum.all?(Map.values(degrees), fn v -> v == 0 end)
Map.keys(map) |> Enum.map(&to_string/1)

Good

Enum.all?(degrees, fn {_k, v} -> v == 0 end)
Enum.map(map, fn {k, _v} -> to_string(k) end)