What does uint8(3) mean as a function signature?

[eulerbeat5]

euler-contracts/contracts/BaseModule.sol

Line 42 in cd3036e

uint8(3),

[hoytech]

Hi! Here, the number 3 should be interpreted as a uint8, which then is encodePacked into a single byte. So this is basically gluing 0x03 onto the beginning of the call-data.

In answer to your question, when proxies are invoked from their "parent" (ie the main euler contract), they use a special non-standard calldata encoding. The 3 here indicates that there are 3 arguments to log (including the Transfer signature). The full details are here: https://docs.euler.finance/developers/proxy-protocol#module-greater-than-proxy