catch and throw

catch is a compiler keyword, not an efun, even though a man page also lives under efun/calls/catch. It evaluates a body and returns 0 on success or the error value on failure.

Two forms share the grammar of time_expression:

mixed err = catch(expr);
mixed err = catch {
    statement;
    statement;
};

The value of a successful body is discarded. Driver errors become a string that starts with *. throw(value) returns that value from the nearest catch. throw(0) cannot be distinguished from "no error", because catch already uses 0 for success.

mixed err = catch(load_object("/obj/missing"));
if (err)
    write("load failed: " + err + "\n");

mixed err = catch {
    foreach (string file in files)
        load_object(file);
};

break and continue may not leave a catch block (compile error). catch is not cheap — use it where an error would corrupt state, not around every line.

await is illegal inside catch(...). In an async function use acatch instead; see async.

Related efuns: error, throw. Master apply: error_handler.