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Erlang / Erlang Advanced Interview questions

When should you use throw instead of returning an {error, Reason} tuple?

Both signal "this didn't work," but they fit different shapes of control flow. A tagged {error, Reason} return keeps the failure visible in the function's ordinary return value, forcing every caller to explicitly pattern-match and decide what to do — it composes naturally with Erlang's usual "match on the result" style and is easy to trace just by reading the function's uses.

%% error tuple: caller must explicitly handle both branches
case validate(Input) of
    {ok, Value} -> proceed(Value);
    {error, Reason} -> reject(Reason)
end.

%% throw: useful for bailing out from deep inside nested helper calls
validate_all(Items) ->
    try [validate_one(I) || I <- Items]
    catch throw:{invalid, Item} -> {error, {invalid, Item}}
    end.

throw earns its keep specifically when you're several calls deep inside a purely internal helper chain and want to bail out immediately to one handler at the top, without threading an {error, Reason} check through every intermediate function in between. It should stay internal to code you also control the corresponding catch for, rather than being part of a module's public API contract, where a tagged tuple is the more discoverable, idiomatic choice.

What is the main advantage of {error, Reason} tuples over throw for a public API?
When does throw earn its keep over threading error tuples through every call?

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