• Error Message
• Error Details
• Methods

An error object, err, can be returned by a function to indicate failure.

$err() -> err
$err(message: any) -> err
$err(format_string: str, arg1: any, arg2: any, ...) -> err

Creates a new err object. Every err has a message string and a details map.

• If called with no arguments, returns an error with an empty message string.
• If called with a single argument, stringifies that argument and uses the result as the error's message string.
• Calling this function with more than one argument is equivalent to calling $fmt() on those arguments first and using the result as the error's message string.

You can use the $is_err(arg) function to check if a value is an err. Alternatively, you can use the error-coalescing operator !! to supply a default value for an operation that might return an error:

var foo = might_fail() !! "default";

Error Message

Stringifying an error returns its message:

var err = $err("oh no!");
assert $str(err) == "oh no!";

Error Details

Every error object contains a details map which you can use to store arbitrary data about the error. You can index into this details map directly on the err object itself, e.g.

var err = $err("disaster strikes!");
err["code"] = 123;

assert $str(err) == "disaster strikes!";
assert err["code"] == 123;

The details map of an err object returned by a try expression contains "source" and "line" entries specifying the source ID and line number of the panic.

Methods

:details() -> map

Returns the error's details map.

:message() -> str

Returns the error's message string.