Virtual balanceOf in ERC20

[ebulku]

🧐 Motivation
I want to use my own logic behind the balanceOf() function for ERC20.

📝 Details
Is there any known issue if I change the balaceOf() in virtual in ERC20.sol

[frangio]

It depends on what you want to override it with. There are potential issues integrating with other contracts when balanceOf returns a dynamic value. I'm not sure if this has been explained anywhere. I couldn't find a link to provide, sorry!

[frangio]

For the general issue of having virtual view functions see #2154.

Closing this issue but let's continue the discussion if you want.

[ebulku]

@frangio There are cases when the balance is changing over time, and to save costs for transactions you can implement the changed balance dynamically. This usually occurs in DeFi when users are getting interests, or there may be cases when the token holders are awarded extra tokens.

I have seen this implementation in aave: https://github.com/aave/aave-protocol/blob/f7ef52000af2964046857da7e5fe01894a51f2ab/contracts/tokenization/AToken.sol#L338

But they are using an older version of OpenZeppelin to override the balanceOf

[ebulku]

@frangio what do you think about this?

[frangio]

@ebulku We're going to add virtual view functions in the next release (see #2154 (comment)). Whether balanceOf will be one of these virtual view functions I'm still not sure. I will try to make it so but there are some caveats (see #2154 (comment)). I've included your request for ERC20.balanceOf in the list of requested virtual functions.