Contract factory example

[lock9]

Hi,
How can I create a contract that creates other contract?
I want to allow my smart-contract to vote, but I want to be able to split their votes into multiple candidates. For that to work, I need to deploy one smart contract per candidate.

I would like to know the best way to create and deploy these 'child' contracts. Is there any kind of constructor concept or equivalent feature? Is there an example?

[shargon]

The problem that the hash is based on NefFile and sender, so if you have the NefFile static, you won't be able to deploy multiple contracts with the same file/sender, I think that we can change from sender to TX.Hash

[erikzhang]

My solution is that we can change the way of generating contract hash.

First, we can add a nonce to nef file. Then the contract hash will be:

contract_hash = hash160(ABORT, sender, checksum(nef))

[lock9]

Will that work Erik? How can we change the nonce before deploying the new contract? (from a smart contract)

Can't we add some sort of constructor? We need a way to customize the deployed contract. I know that we can dismiss the need for a constructor if we add the initialization methods ourselves and call it when we deploy the contract.

[erikzhang]

How can we change the nonce before deploying the new contract? (from a smart contract)

Use NEWBUFFER, MEMCPY, CAT, SUBSTR.

Or we can add a new method CreateChild() in ContractManagement?

[lock9]

Use NEWBUFFER, MEMCPY, CAT, SUBSTR.

I'm in favor of a more 'developer-friendly' solution. It is too dangerous to change bytes 'manually'. Maybe the second option is better.

[roman-khimov]

Maybe we just take the name from the manifest and add it into the hash mix? This will require preparing a number of manifests, but that should be feasible and I think one would like to have these contracts have different names anyway (like NeoFS alphabet contracts, https://github.com/nspcc-dev/neofs-spec/blob/master/02-blockchain/01-governance.md). Though it makes upgrade somewhat more complicated.

Another option could be adding an explicit name parameter to override (and replace) the one we have in the manifest.

[shargon]

Why not use the Transaction hash?

[erikzhang]

Why not use the Transaction hash?

Because you can't compute the hash at the compile time.

[shargon]

Because you can't compute the hash at the compile time.

Then we can use a nonce based on the data (#2239).

[erikzhang]

Then we can use a nonce based on the data (#2239).

But there is no standard on the data.

[shargon]

Add a new field on Deploy?

[erikzhang]

Too many fields. What about add CreateChild()? It create a cloned contract with different hash.

[Tommo-L]

Maybe we can do it like this.

Upload -> Contract Nef file ---- instantiation(+add params to invoke deploy method) --->  Contract A
                            ---- instantiation ----> Contract B