No Common Caveats

Usage of functions that are known to be inefficient or ambiguous, when more efficient or explicit alternatives are available, should be avoided.

This rule also follows the recommendations from the Erlang Efficiency Guide – Common Caveats, and warns when these suboptimal functions are used.

Rationale

Some standard library functions, while valid, have performance drawbacks or implicit behavior that can lead to subtle bugs or inefficiencies—especially in performance-critical code. Replacing them with clearer or better-scaling alternatives tends to make systems easier to reason about and to tune.

Rationale for default caveat_functions

The built-in list exists so new users get guardrails aligned with Erlang/OTP guidance; you can always narrow or extend it in configuration.

• timer:send_after/2,3 and timer:send_interval/2,3 — Traffic for the timer module goes through a dedicated process; the efficiency guide recommends erlang:start_timer/3,4 and erlang:send_after/3,4 for better scalability and clearer semantics in many designs.
• erlang:size/1 — Works on both tuples and binaries; tuple_size/1 and byte_size/1 make intent explicit and allow the compiler to optimize better.
• gen_server:call/2, gen_statem:call/2, and gen_event:call/3 — The two-argument (or three-argument for gen_event) forms use a default timeout of infinity, so a stuck peer can block the caller indefinitely. Prefer the variants with an explicit timeout unless you truly need to wait forever.
• erlang:list_to_atom/1 and erlang:binary_to_atom/1,2 — Every new atom is interned for the life of the node; unbounded creation (e.g. from user input) can exhaust the atom table. Prefer list_to_existing_atom/1, binary_to_existing_atom/1,2, maps, or binaries when identifiers are dynamic.
• erlang:garbage_collect/0 — Forces a full collection on the calling process and can inject noticeable latency spikes; the runtime usually schedules GC well on its own, so this call should be rare and deliberate (added in 5.0.0).

{gen_statem, call, 2}, {gen_server, call, 2}, {gen_event, call, 3}, {erlang, list_to_atom, 1}, {erlang, binary_to_atom, 1}, and {erlang, binary_to_atom, 2} were added in 4.1.0.

Options

• caveat_functions :: [{module(), function(), arity()} | {module(), function()}]

  • default: [{timer, send_after, 2} , {timer, send_after, 3} , {timer, send_interval, 2} , {timer, send_interval, 3} , {erlang, size, 1} , {gen_statem, call, 2} , {gen_server, call, 2} , {gen_event, call, 3} , {erlang, list_to_atom, 1} , {erlang, binary_to_atom, 1} , {erlang, binary_to_atom, 2} , {erlang, garbage_collect, 0} ]

Example configuration

{elvis_style, no_common_caveats_call, #{
    caveat_functions => [
        {timer, send_after, 2},
        {timer, send_after, 3},
        {timer, send_interval, 2},
        {timer, send_interval, 3},
        {erlang, size, 1},
        {gen_statem, call, 2},
        {gen_server, call, 2},
        {gen_event, call, 3},
        {erlang, list_to_atom, 1},
        {erlang, binary_to_atom, 1},
        {erlang, binary_to_atom, 2}
    ]
}}