Are smart contract fields private?

[stone sand]

For example

// is the field x private?
class Ex extends SmartContract {
  ...
  x = new UInt32(42);
  ...
}

[alpine dirge]

x, in your example, is private. It's not on chain. But it's also not useful in a proof context.

ex = new Ex();
ex.x = UInt32.from(5);
ex.x = UInt32.from(10000);

There's no constraints on the value

[stone sand]

Thanks!

Does this mean the value can be manipulated at verification time irregardless of a proof?

[alpine dirge]

Not sure what you mean by at verification time. If you wanted to include it in a @method, you'd probably have to wrap the call in a Circuit.asProver context. I would call that an anti-pattern.

But I could imagine manipulating it, for example, after a transaction is sent, you could increment transactionCount on your smart contract instance. I can't think of too many examples where it's useful. Pretty much x in your example is a property on a typescript class just like any other property on a typescript class. But it's totally unrelated to any functionality of a smart contract.

[stone sand]

Verification time (when a node verifies the proof) as opposed to proving time (when the contract client generates the proof)

Thank you!

[alpine dirge]

The verifier will not have access to the property x in your example. x is a property that only exists on the typescript class which lives, for example, in the user’s browser as they create a proof. It’s not reflected in the proof itself that gets sent to the network for verification.

[stone sand]

Okay, nice! Thanks for that

[spice granite]

Actually, x will not be stored in-chain, but it will be “hard coded” into the circuit, so it can’t be manipulated. And in order to execute the contract, users need the source code - so you’ll have to share the code and the value of x nonetheless

[alpine dirge]

Best way to learn an answer to something is write something incorrect on the internet 🙂

[stone sand]

That's exactly what I was expecting!
Is there a better way to provide initial parameters to a contract in order for these values to be effectively baked into the @method call? (instead of requiring clients to be in possession of the source code)

[spice granite]

Users will always need to have the source code in order to execute the contract and produce a valid proof

[stone sand]

Solves that mystery. Thank you!

[alpine dirge]

@spice granite is there a good example of where a property like that would be useful?

[spice granite]

ye, like hard coding a constant in e.g. a DEX or more generally specifying a privileged public key that is only allowed to access some functionality

[stone sand]

I am thinking of a game with a fixed cost for making a move. I want the cost to be hardcoded in any given instance of the contract, a parameter amongst the instances, and not stored on chain.