You've detected that the integer value of argument x passed to the current function is invalid. Write the idiomatic way to abort the function execution and signal the problem.
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Other implementations
enum {

int square(int x, int *result) {
    if (x > 1073741823) {
        return E_OUT_OF_RANGE;
    *result = x*x;
    return E_OK;
throw domain_error("oops!");
throw new ArgumentException(nameof(×));
import std.format;
throw new Exception("invalid value for x (%s) in '%s'".format(x, __PRETTY_FUNCTION__));
void foo(int x)
    assert(x != 0, "wrong value for x");
    // function
  if (x > largest_value) error stop "Illegal value in function."
return nil, fmt.Errorf("invalid value for x: %v", x)
throw new IllegalArgumentException("Invalid value for x: $x")
sqrt' :: Int -> Either String Int
sqrt' x | x < 0 = Left "Invalid argument"
sqrt' x         = Right (sqrt x)
throw new Error ('x is invalid')
throw new IllegalArgumentException("Invalid value for x:" + x);
error("Invalid argument x")
return nil, "Invalid argument x"
throw new \InvalidArgumentException($x . ' is invalid.');
Uses sysutils, math;
Raise EInvalidArgument.CreatFmt('Invalid value: %d',[x]);
die "Invalid argument $x";
raise ValueError("x is invalid")
raise ArgumentError, "invalid value #{x}."
enum CustomError { InvalidAnswer }

fn do_stuff(x: i32) -> Result<i32, CustomError> {
    if x != 42 {
    } else {