# transfer & mint
## Overview
* [x] cache
* [x] updateState
* [x] validateSupply
* [x] updateInterestRates
* [ ] transfer & mint
* [ ] If isFirstSupply
{% hint style="info" %}
updateInterestRates was covered in the common functions section
{% endhint %}
### transfer
{% code overflow="wrap" %}
```solidity
IERC20(params.asset).safeTransferFrom(msg.sender, reserveCache.aTokenAddress, params.amount);
```
{% endcode %}
This transfers the asset to be supplied from user to the corresponding AToken contract
* from: `msg.sender`
* to: `aTokenAddress` (aDAI, aWETH...)
{% hint style="info" %}
User' supplied assets are held on their respective AToken contracts; DAI held on aDAI.
{% endhint %}
{% hint style="info" %}
**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](https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729) possible with vanilla `approve`.
For more:
{% endhint %}
### mint
* minting of ATokens corresponding the supplied asset
{% code overflow="wrap" %}
```solidity
bool isFirstSupply = IAToken(reserveCache.aTokenAddress).mint(msg.sender, params.onBehalfOf, params.amount, reserveCache.nextLiquidityIndex);
```
{% endcode %}
* `mint` calls `_mintScaled`
* `_mintScaled` mints tokens in-line with the current liquidity index, as seen by `amountScaled`
* `amountToMint`: `amountScaled`cast 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`
{% hint style="info" %}
`additionalData` in the context of Atokens
* used to store the index of the user's last "index-sensitive" action: --> last supply/withdrawal/borrow/repayment
{% endhint %}
#### 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
