transfer & mint

Overview

• cache

• updateState

• validateSupply

• updateInterestRates

• transfer & mint

• If isFirstSupply

updateInterestRates was covered in the common functions section

transfer

IERC20(params.asset).safeTransferFrom(msg.sender, reserveCache.aTokenAddress, params.amount);

This transfers the asset to be supplied from user to the corresponding AToken contract

• from: msg.sender

• to: aTokenAddress (aDAI, aWETH...)

User' supplied assets are held on their respective AToken contracts; DAI held on aDAI.

Use of safeTransferFrom

SafeERC20 is a helper to make safe the interaction with someone else’s ERC20 token, in your contracts. What the helper does for you is:

1. check the boolean return values of ERC20 operations and revert the transaction if they fail,

2. at the same time allowing you to support some non-standard ERC20 tokens that don’t have boolean return values.

It additionally provides helpers to increase or decrease an allowance, to mitigate an attack 118 possible with vanilla approve.

For more: https://forum.openzeppelin.com/t/making-sure-i-understand-how-safeerc20-works/2940

mint

• minting of ATokens corresponding the supplied asset

bool isFirstSupply = IAToken(reserveCache.aTokenAddress).mint(msg.sender, params.onBehalfOf, params.amount, reserveCache.nextLiquidityIndex);

• mint calls _mintScaled

• _mintScaled mints tokens in-line with the current liquidity index, as seen by amountScaled

• amountToMint: amountScaledcast as uint128

• balanceIncrease: interest accrued from user's last recorded index and current index

• _userState[onBehalfOf].additionalData is updated with the latest index.

balanceIncrease is calculated as part of the mint event emission.

On super.BalanceOf and _userState[onBehalfOf].additionalData

• super.BalanceOf calls balanceOf declared in IncentivizedERC20.sol

• Inheritance: ScaledBalanceTokenBase > MintableIncentivizedERC20 > IncentivizedERC20

• notice the irregular definition of balanceOf, it calls out a mapping _userState

• _userState is mapping of user addresses to UserState structs

• Each UserState struct stores a user's balance with a wildcard field of additionalData

additionalData in the context of Atokens

• used to store the index of the user's last "index-sensitive" action: --> last supply/withdrawal/borrow/repayment

Returns

mint returns the bool value of (scaledBalance == 0)

• scaledBalance is the amount of balance a user has of a specific asset pre-dating this supply action

• (scaledBalance == 0) will return true only if this supply action is the user's very first supply action - specific to said asset.

• The return bool value is useful to us as explained in the next section.

Visual Aid