Calling Smart Contracts

Smart contracts are not very useful in isolation, they typically interact with other smart contracts that make up the building blocks of a larger piece of infrastructure.

Calling One of Your Smart Contracts

Calling another one of your smart contracts requires using LinkedSmartContract.for. Given the following contract in Foo.ts:

export class Foo extends SmartContract {
  public takeAction(): boolean {
    return true;
  }
}

We can get the singleton instance of Foo using LinkedSmartContract.for<Foo>():

import { Foo } from './Foo';

export class Bar extends SmartContract {
  public callOtherContract(): boolean {
    const foo = LinkedSmartContract.for<Foo>();
    return foo.takeAction();
  }
}

Once we have an instance of the contract we can access any of its public properties and methods. Events from the original contract are also propagated automatically and are made available in the NEO•ONE client APIs.

Calling an Arbitrary Smart Contract

Continuing from the examples above, let’s say we want to invoke the takeAction method of a smart contract at a given arbitrary Address. Similar to LinkedSmartContract.for, we can get the instance of the smart contract using SmartContract.for<Foo>(address) where address is the Address of the smart contract:

interface Foo {
  readonly takeAction: () => boolean;
}
declareEvent<string>('actionTaken', 'value');

export class Bar extends SmartContract {
  public callOtherContract(address: Address): boolean {
    const foo = SmartContract.for<Foo>(address);
    return foo.takeAction();
  }
}

Notice that we also have to define the interface of the smart contract explicitly. The instance returned by SmartContract.for will match the interface we’ve defined and then we can access any of its public properties and methods.

We also have to declare the events we expect to be emitted by the underlying contract explicitly using declareEvent. The declareEvent method works the same as createEventNotifier except it does not return a function that can be called to emit an event. Instead, it just informs the NEO•ONE toolchain that there are additional events that it needs to register with the NEO•ONE client APIs.

Note

A common, but advanced, usage pattern for invoking other arbitrary smart contract is to forward argument values to the invoked method. See the advanced guide on Forward Values to learn more.