With TRUFFLE: Call public function of contract from within another contract

Question

Similar to How do you call a function of a deployed contract from another contract? (first answer), but because Truffle has access to the ABI's of compiled contracts thought I could avoid low-level call

Want to call a public function timeProtectTokens on token variable representing ERC20 contract within Escrow contract. Intuitively I thought to do:

 let token = await ERC20.new() let escrow = await Escrow.new(token.address) let result = await escrow.token.timeProtectTokens(initialAccount, 5)

..but fails

contract ERC20 is Protected { } import "./ERC20.sol"; contract Escrow { ERC20 public token; constructor(ERC20 _token) public { token = _token; } } contract Protected { mapping (address => uint256) public protectedTokens; function timeProtectTokens(address _address, uint256 _amount) public **onlyEscrow** { protectedTokens[_address] = protectedTokens[_address].add(_amount); } }

goodvibration · Accepted Answer · 2020-03-13 22:51:14Z

You cannot do it this way.

First, you need to do const tokenAddress = await escrow.token();.

Then, you need to use this address in order to create a contract object.

If you're on Truffle v4.x (web3.js v0.x), then you can do:

const tokenContract = web3.eth.contract(<Your ERC20 ABI Array>).at(tokenAddress);

If you're on Truffle v5.x (web3.js v1.x), then you can do:

const tokenContract = new web3.eth.Contract(<Your ERC20 ABI Array>, tokenAddress);

But I believe that you might experience problems interacting with your contract within Truffle tests.

So alternatively, you should probably use @truffle/contract.

Following that, you should finally be able to do:

const result = await tokenContract.timeProtectTokens(initialAccount, 5);

Syntax I'm using (ie ERC20.new()) is truffle-contract... I'd prefer to use truffle-contract because this for a test issue (timeProtectTokens uses OZ's Roles contract modifier, requiring that the call originate from the Escrow Contract, not a user account ) — Zach_is_my_name
– Zach_is_my_name, Commented Mar 13, 2020 at 22:18

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