implement erc20 reducer, transfers

[nionis]

This implementation is only for transfers, we need to discuss on what is the best way to handle mints / burns / totalSupply

[shrugs]

For handing mint/burn mechanics, lets implement the minimum viable concept of

1. If Transfer to 0x0 or Mint, add the value to the addr and emit a ERC20_MINT reason.
2. If Transfer from 0x0 or Burn, subtract the value from the addr and emit an ERC20_BURN reason.

That should get us 90% of compatibility, I think. Let's use the OpenZeppelin Burn and Mint event abis.

[nionis]

@shrugs should we make 0x0 balance to remain 0 when there its Transfer from 0x0 to X address ?

[shrugs]

@nionis It seems like an arbitrary thing, but I do prefer the idea of keeping burns literal. That way we should be able to get totalSuppy by doing something like SELECT SUM(balance) as totalSupply where address = '0xabcd'.

[nionis]

@shrugs Mint / Burn always emit Transfer function, so there is no need to check for those events unless we want to specifically store the MINT_REASON or BURN_REASON

so I would just look for Transfer event, and then check from / to values, if they are 0x0 then I do MINT_REASON / BURN_REASON

sounds good?

[shrugs]

Yup! There might be edge cases with some tokens that don't emit the correct transfer event, but I expect it's not something we have to worry about yet.

Let's definitely note that the reason being different between transfers mints and burns; that's something i expect people would like to query directly, instead of inferring it from the fact that the _to is 0 or vise versa.

-matt

On Fri, Aug 3, 2018, 11:32 Steve notifications@github.com wrote:

@shrugs https://github.com/shrugs Mint / Burn always emit Transfer function, so there is no need to check for those events unless we want to specifically store the MINT_REASON or BURN_REASON

so I would just look for Transfer event, and then check from / to values, if they are 0x0 then I do MINT_REASON / BURN_REASON

sounds good?

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