Throwing Exceptions

Exceptions in Coco signal failures during endpoint execution. You can throw a plain String, or throw a class instance whose except() special method produces the error message. When an exception is thrown, execution stops immediately and the error is returned to the caller; any subsequent code in the endpoint is skipped. Use exceptions for invariant violations and permission checks rather than control flow.

coco Throw
class Person:
    field age U64

    method adult() -> (is_adult Bool):
        is_adult = self.age >=18

    method __except__() -> (err String):
        yield err f"underage: only {self.age} years"

// Simplest way to throw an exception is to just throw a string
endpoint TestThrow(s String):
    throw s

endpoint invoke AgeVerification(age U64):
    memory person = Person{age: age}

    if !(is_adult) <- person.adult():
        throw person.__except__()

Catching Exceptions

try...catch... statement is not implemented in Coco 0.7.0 or PISA 0.5.0