Raises an assert_err() if the specified expression evaluates to false.

This function does not generate a change.


assert(expression [, error_msg])


Argument Type Description
expression any (required) The expression to evaluate.
error_msg str (optional) Custom error message.

Return value

Returns nil if the type of the expression evaluates to true. Otherwise an assert_err() is raised.

In versions before v0.9.4 the return value of assert(..) used to be the return value from the expression (when evaluated as true).


This code shows how assert can be used:

assert(1 > 2, 'one is still smaller than two');

Raises an assert_err() exception

    "error_msg": "one is still smaller than two",
    "error_code": -50