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W0064 - Use ets:lookup_element/4 instead of case ets:lookup/2

Warning​

read(Tab, Key) ->
    case ets:lookup(Tab, Key) of
%%  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 💡 W0064: Can be rewritten using `ets:lookup_element/4` for improved performance.
        [{_, V}] -> V;
        _ -> undefined
    end.

Explanation​

The warning indicates that you are using ets:lookup/2 in a case expression that immediately destructures the result to extract the second element of the tuple or return a default value. This pattern allocates an intermediate list and tuple that are immediately discarded.

Since OTP 26.2, ets:lookup_element/4 accepts a fourth argument as a default value to return when the key is not found, making this a direct replacement for the common case ets:lookup(...) pattern.

Why This Matters​

  • Performance: ets:lookup_element/4 avoids allocating the intermediate [{Key, Value}] list and tuple
  • Readability: A single function call is clearer than a case expression with two clauses
  • Idiomatic Erlang: ets:lookup_element/4 is the idiomatic way to look up a value with a default since OTP 26.2

Patterns Detected​

The diagnostic detects all of these equivalent forms:

%% Wildcard key, wildcard default
case ets:lookup(Tab, Key) of
    [{_, V}] -> V;
    _ -> Default
end

%% Wildcard key, empty list default
case ets:lookup(Tab, Key) of
    [{_, V}] -> V;
    [] -> Default
end

%% Empty list clause first
case ets:lookup(Tab, Key) of
    [] -> Default;
    [{_, V}] -> V
end

%% Key re-checked in tuple (redundant but common)
case ets:lookup(Tab, Key) of
    [{Key, V}] -> V;
    _ -> Default
end

Fix​

Replace the case expression with a call to ets:lookup_element/4:

read(Tab, Key) ->
    ets:lookup_element(Tab, Key, 2, undefined).

The third argument (2) refers to the position of the value in the ETS tuple (the first element is the key at position 1).

See Also​