ABC Size

Functions should not have excessively high ABC size.

The ABC size metric measures function size as a vector of three components:

• A (Assignments): Count of match (=) expressions
• B (Branches): Count of function calls
• C (Conditions): Count of branching clauses (beyond the first in case/if/receive/try/maybe), andalso/orelse operators, and comparison operators (==, /=, =:=, =/=, <, >, =<, >=)

The final score is the vector magnitude: sqrt(A^2 + B^2 + C^2).

Anonymous functions are not counted as part of the enclosing function's ABC size.

Avoid

big_function(Input) ->
    X1 = lists:seq(1, Input),
    X2 = lists:map(fun(X) -> X + 1 end, X1),
    X3 = lists:filter(fun(X) -> X > 5 end, X2),
    X4 = lists:sum(X3),
    X5 = lists:reverse(X2),
    X6 =
        case X4 > 100 andalso X4 < 1000 of
            true ->
                io:format("range: ~p~n", [X4]),
                X4 * 2;
            false ->
                0
        end,
    {X5, X6}.

Prefer

Break large functions into smaller ones with fewer assignments, calls, and conditions:

process(Input) ->
    Numbers = transform(Input),
    format_result(Numbers).

transform(Input) ->
    X1 = lists:seq(1, Input),
    X2 = lists:map(fun(X) -> X + 1 end, X1),
    lists:filter(fun(X) -> X > 5 end, X2).

format_result(Numbers) ->
    Total = lists:sum(Numbers),
    scale(Total).

Rationale

A high ABC size indicates a function that does too much: too many variable bindings, too many function calls, or too many conditional paths. Splitting such functions into smaller, more focused units improves readability and testability.

Options

• max_abc_size :: number()
  • default: 30

Example configuration

{elvis_style, abc_size, #{max_abc_size => 30}}