Fuels-ts

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Instantiating predicates ​

A predicate in Sway can be as simple as the following:

rust
predicate;

fn main() -> bool {
    true
}
See code in context

In this minimal example, the main function does not accept any parameters and simply returns true.

Just like contracts in Sway, once you've created a predicate, you can compile it using forc build. For more information on working with Sway, refer to the Sway documentation.

After compiling, you will obtain the binary of the predicate and its JSON ABI (Application Binary Interface). Using these, you can instantiate a predicate in TypeScript as shown in the code snippet below:

ts
import { FUEL_NETWORK_URL, Provider, Predicate } from 'fuels';

const provider = await Provider.create(FUEL_NETWORK_URL);
const predicateParams: PredicateParams = {
  bytecode: binary,
  provider,
  abi: jsonAbi,
};
const predicate = new Predicate(predicateParams);
See code in context

The created Predicate instance, among other things, has three important properties: the predicate bytes (byte code), the chainId, and the predicate address.

This address, generated from the byte code, corresponds to the Pay-to-Script-Hash (P2SH) address used in Bitcoin.

Predicate with multiple arguments ​

You can pass more than one argument to a predicate. For example, this is a predicate that evaluates to true if the two arguments are not equal:

rust
predicate;

fn main(arg1: u64, arg2: u64) -> bool {
    return arg1 != arg2;
}
See code in context

You can pass the two arguments to this predicate like this:

ts
const predicate = new Predicate({
  bytecode: predicateBytesMulti,
  abi: predicateAbiMulti,
  provider,
  inputData: [20, 30],
});
const tx = await predicate.transfer(receiver.address, amountToReceiver, baseAssetId, {
  gasLimit: 1000,
});
const { isStatusSuccess } = await tx.waitForResult();
See code in context

Predicate with a Struct argument ​

You can also pass a struct as an argument to a predicate. This is one such predicate that expects a struct as an argument:

rust
predicate;

struct Validation {
    has_account: bool,
    total_complete: u64,
}

fn main(received: Validation) -> bool {
    let expected_has_account: bool = true;
    let expected_total_complete: u64 = 100;

    received.has_account == expected_has_account && received.total_complete == expected_total_complete
}
See code in context

You can pass a struct as an argument to this predicate like this:

ts
const predicate = new Predicate<[Validation]>({
  bytecode: predicateBytesMainArgsStruct,
  abi: predicateAbiMainArgsStruct,
  provider,
  inputData: [{ has_account: true, total_complete: 100 }],
});
const tx = await predicate.transfer(receiver.address, amountToReceiver, baseAssetId, {
  gasLimit: 1000,
});
const { isStatusSuccess } = await tx.waitForResult();
See code in context