Predicates, in Sway, are programs that return a Boolean value, and they do not have any side effects (they are pure).

Instantiating predicates

Once you've written a predicate in Sway and compiled it with forc build, you can use the abigen! to generate all the types specified in the predicate. Additionally, you will get a predicate instance with methods for receiving and spending funds and encoding the predicate data. The code snippet below shows how to use the abigen and generate a predicate instance.

        abigen!(Predicate(name="MyPredicate", abi="packages/fuels/tests/predicates/predicate_signatures/out/debug/predicate_signatures-abi.json"));

        let predicate = MyPredicate::load_from(

The predicate address is generated from the compiled byte code and is the same as the P2SH address used in Bitcoin. Users can seamlessly send assets to the predicate address as they do for any other address on the chain. To spend the predicate funds, the user has to provide the original byte code of the predicate together with the predicate data. The predicate data will be used when executing the byte code, and if the predicate is validated successfully, the funds can be transferred.

In the next section, we show how to interact with a predicate and explore an example where specific signatures are needed to spend the predicate funds.