Asserting

Assertions can be used to ensure a certain condition is met when running a contract. The predefined function assert is used to check whether a given a Boolean condition holds. The function assert_some is used to check if an option value is not None. The function assert_some_with_error is like assert_some but an error message can be given. Whenever the assertion fails, the contract will stop and an error will be left on the execution stack.

const incr_if_true = (b: bool, n: int) : int => {

assert(b);

return n+1;

};

const incr_if_some = (b: option<unit>, n: int) : int => {

assert_some(b);

return n+1;

};

You can use assert_with_error or assert_some_with_error to use a custom error message.

const incr_if_true = (b: bool, n: int) : int => {

assert_with_error (b, "My custom error message.");

return n+1;

};

Likewise, we can check for None instead of Some by using assert_none and assert_none_with_error.