Writing and Calling a Rust Contract

One of the benefits of using PolkaVM vs EVM is that you can write contracts in any language that compile down to RISC-V. In this chapter we learn how to use Rust to write a contract and how to call it from Solidity.

Use the Rust Template

Here you can find our Rust contract template. You can make use of githubs template feature in order to make it the starting point of your own repository.

Compile the template

Simply follow the README inside the template to learn how to compile the project into a contract.polkavm. The repository also contains a example Solidity file that demonstrates how to call this contract.

Deploy the template

You can use ether.js to deploy the Rust contract. We covered that earlier in the tutorial. You skip the compilation step and pass the raw contract.polkavm as bytecode:

import { ContractFactory } from 'ethers'

/// We specify the abi manually since the Rust compiler won't generate one for us
const abi = ["constructor()", "function fibonacci(uint) view returns(uint)"];
const bytecode = readFileSync('contract.polkavm');

// Instantiate a contract factory.
const contractFactory = new ContractFactory(abi, bytecode, signer)

try {
  const contract = await contractFactory.deploy(/* args */)
  await contract.waitForDeployment()

  // Get the contract's address.
  const address = await contract.getAddress()
  console.log(`Contract deployed: ${address}`)
} catch (e) {
  console.error('Failed to deploy contract', e)
}

// Try calling the fibonacci function directly
// ...

Deploy and Use the Caller Contract

You can now deploy the Solidity contract from the template repository using ether.js or REMIX. It is setup to call the Rust contract via the fibonacciRust function. You need to pass the address from the previous step.