feat: errors

[julio4]

Close #6
I'm considering adding another practical example of a simple vault contract with a deposit and withdraw function. Please let me know if you think it's a good idea.

Additionally, I have included some security considerations that I believe are important to keep in mind. Please let me know if you find this kind of content useful.

[enitrat]

This is very good, however I'm a bit worried that this is a bit out of scope of just CairoByExample and some of this content should be in the cairo book instead. Especially this part

Security Considerations
Transactions in smart contracts are atomic, meaning they either succeed or fail without making any changes.
Think of smart contracts as state machines: they have a set of initial states defined by the constructor constraints, and external function represents a set of possible state transitions. A transaction is nothing more than a state transition.
Using errors to check conditions adds constraints that helps clearly define the boundaries of possible state transitions for each function in your smart contract. These checks ensure that the behavior of the contract stays within the expected limits.
By incorporating these concepts during development, you can create robust and reliable smart contracts. This reduces the chances of unexpected behavior or vulnerabilities.

I think it would be better to have this in-depth explanation part in the Cairo Book directly, and here give a very succint description and advanced example of how to use errors and condition checks in smart contracts.

I'm considering adding another practical example of a simple vault contract with a deposit and withdraw function.

Yes, it's an excellent idea.
Another thing you could do is demonstrate how we could create group errors together in an error module, and then refer to them from there.

mod Errors{
  const BALANCE_TOO_LOW = 'user balance is too low';
}

#[contract]
mod Vault{
 fn withdraw(){
  ///
  assert(amount<=balance, Errors::BALANCE_TOO_LOW);
 }
}

[julio4]

This is very good, however I'm a bit worried that this is a bit out of scope of just CairoByExample and some of this content should be in the cairo book instead.

I agree. I might want to explain too much because I'm also learning at the same time. I'll try to keep things simple and move in-depth explanations to the Cairo book if I think it's interesting content.

[enitrat]

I'll try to keep things simple and move in-depth explanations to the Cairo book if I think it's interesting content.

🔥

[enitrat]

LGTM 🔥