AssertionError

Built-in class · Extends Error

An AssertionError is what a failed assert raises. It extends Error directly, not RuntimeError, so catch error: RuntimeError does not catch it: a failed check is a mistake in the program, not something to handle along the way.

try {
    assert 1 + 1 == 3
}
catch error: AssertionError {
    print(error.message)     # prints assertion failed: `1 + 1 == 3`
}

message: String

The message written in the assert, or, when there was none, the condition that failed: assertion failed: `1 + 1 == 3` .