not considering `ERC20.transfer()` returning `false` about v1-contracts

[haydenadams]

@daejunpark
Good point, thanks for the feedback. One potential issue is that many ERC20s are not fully ERC20 compliant (over 130 on EtherDelta) and do not return a bool at all, so this assertion might make those token transfers to fail. I'll write a test for it.

The only way I can think of that covers all cases is something like this:

user_balance: uint256 = Token(self.token).balanceOf(msg.sender)
self.token.transfer(msg.sender, tokens_purchased)
assert Token(self.token).balanceOf(msg.sender) == user_balance - tokens_purchased

Probably not even that bad a gas hit either!

[haydenadams]

I decided to go with assert self.token.transfer(msg.sender, tokens). Tokens that do not return True will need to be wrapped.

[BlinkyStitt]

Is there a recommend way of doing this wrapping in Vyper? I’ve seen some solutions in solidity.

[jacqueswww]

Just for info: Vyper has assert_modifiable for this purpose now.