Aave V3 Tokenization on Aptos

Reference for the aave-tokens Move package.

This documentation covers the tokenization modules in the Aave protocol implementation on Aptos. Similar to Aave on EVM chains, the Aptos implementation uses specialized tokens to represent user positions in the protocol.

aToken Factory

The a_token_factory module manages the creation and operations of aTokens, which represent user supply positions in the Aave protocol. aTokens are interest-bearing tokens that automatically accrue interest to their holders.

Write Methods

create_token

public(friend) fun create_token(
    signer: &signer,
    name: String,
    symbol: String,
    decimals: u8,
    icon_uri: String,
    project_uri: String,
    incentives_controller: Option<address>,
    underlying_asset: address,
    treasury: address
): address

Creates a new aToken for a specific underlying asset.

Input Parameters:

Return Values:

Emits:

• Initialized event with details about the created aToken

mint

public(friend) fun mint(
    caller: address,
    on_behalf_of: address,
    amount: u256,
    index: u256,
    metadata_address: address
): bool

Mints aTokens to a user.

Input Parameters:

Return Values:

burn

public(friend) fun burn(
    from: address,
    receiver_of_underlying: address,
    amount: u256,
    index: u256,
    metadata_address: address
)

Burns aTokens from a user and sends the equivalent amount of underlying to the receiver.

In some instances, a mint event could be emitted from a burn transaction if the amount to burn is less than the interest that the user accrued.

Input Parameters:

mint_to_treasury

public(friend) fun mint_to_treasury(
    amount: u256,
    index: u256,
    metadata_address: address
)

Mints aTokens to the reserve treasury.

Input Parameters:

transfer_on_liquidation

public(friend) fun transfer_on_liquidation(
    from: address,
    to: address,
    amount: u256,
    index: u256,
    metadata_address: address
)

Transfers aTokens in the event of a borrow being liquidated, in case the liquidator reclaims the aToken.

Input Parameters:

Emits:

• Balance transfer event with the scaled amount and index

handle_repayment

public fun handle_repayment(
    _user: address,
    _on_behalf_of: address,
    _amount: u256,
    _metadata_address: address
)

Handles the underlying received by the aToken after the transfer has been completed.

The default implementation is empty as with standard tokens, nothing needs to be done after the transfer is concluded. However, in the future there may be aTokens that allow for example to stake the underlying to receive LM rewards. In that case, handle_repayment() would perform the staking of the underlying asset.

Input Parameters:

drop_token

public(friend) fun drop_token(metadata_address: address)

Drops the aToken associated data.

Input Parameters:

View Methods

get_underlying_asset_address

public fun get_underlying_asset_address(
    metadata_address: address
): address

Returns the address of the underlying asset of this aToken.

Input Parameters:

Return Values:

get_previous_index

public fun get_previous_index(
    user: address,
    metadata_address: address
): u256

Returns the last index interest was accrued to the user’s balance.

Input Parameters:

Return Values:

get_scaled_user_balance_and_supply

public fun get_scaled_user_balance_and_supply(
    owner: address,
    metadata_address: address
): (u256, u256)

Returns the scaled balance of the user and the scaled total supply.

Input Parameters:

Return Values:

scaled_balance_of

public fun scaled_balance_of(
    owner: address,
    metadata_address: address
): u256

Returns the scaled balance of the user.

The scaled balance is the sum of all the updated stored balance divided by the reserve’s liquidity index at the moment of the update.

Input Parameters:

Return Values:

scaled_total_supply

public fun scaled_total_supply(
    metadata_address: address
): u256

Returns the scaled total supply of the aToken.

The scaled total supply is the sum of all scaled balances of the users.

Input Parameters:

Return Values:

decimals

public fun decimals(metadata_address: address): u8

Returns the decimals of the aToken.

Input Parameters:

Return Values:

Variable Debt Token Factory

The variable_debt_token_factory module manages the creation and operations of variable debt tokens in the Aave protocol on Aptos. Variable debt tokens represent user borrowing positions with a variable interest rate.

Write Methods

create_token

public(friend) fun create_token(
    signer: &signer,
    name: String,
    symbol: String,
    decimals: u8,
    icon_uri: String,
    project_uri: String,
    incentives_controller: Option<address>,
    underlying_asset: address
): address

Creates a new variable debt token for a specific underlying asset.

Input Parameters:

Return Values:

Emits:

• Initialized event with details about the created variable debt token

mint

public(friend) fun mint(
    caller: address,
    on_behalf_of: address,
    amount: u256,
    index: u256,
    metadata_address: address
): bool

Mints debt tokens to the on_behalf_of address.

Input Parameters:

Return Values:

Emits:

• Transfer event from zero address to recipient

• Mint event with details about the mint operation

burn

public(friend) fun burn(
    from: address,
    amount: u256,
    index: u256,
    metadata_address: address
)

Burns debt tokens from a user.

Input Parameters:

Emits:

• Transfer event to zero address
• Burn event with details about the burn operation
• If the balance increase is greater than the amount, also emits Transfer and Mint events

drop_token

public(friend) fun drop_token(metadata_address: address)

Drops the variable debt token associated data.

Input Parameters:

View Methods

get_underlying_asset_address

public fun get_underlying_asset_address(
    metadata_address: address
): address

Returns the address of the underlying asset of this variable debt token.

Input Parameters:

Return Values:

get_previous_index

public fun get_previous_index(
    user: address,
    metadata_address: address
): u256

Returns the last index interest was accrued to the user’s balance.

Input Parameters:

Return Values:

get_scaled_user_balance_and_supply

public fun get_scaled_user_balance_and_supply(
    owner: address,
    metadata_address: address
): (u256, u256)

Returns the scaled balance of the user and the scaled total supply.

Input Parameters:

Return Values:

scaled_balance_of

public fun scaled_balance_of(
    owner: address,
    metadata_address: address
): u256

Returns the scaled balance of the user.

The scaled balance is the sum of all the updated stored balance divided by the reserve’s variable debt index at the moment of the update.

Input Parameters:

Return Values:

scaled_total_supply

public fun scaled_total_supply(
    metadata_address: address
): u256

Returns the scaled total supply of the variable debt token.

The scaled total supply is the sum of all scaled balances of the users with debt.

Input Parameters:

Return Values:

name

public fun name(metadata_address: address): String

Returns the name of the variable debt token.

Input Parameters:

Return Values:

symbol

public fun symbol(metadata_address: address): String

Returns the symbol of the variable debt token.

Input Parameters:

Return Values:

decimals

public fun decimals(metadata_address: address): u8

Returns the decimals of the variable debt token.

Input Parameters:

Return Values:

Comparison with Ethereum

The variable debt token implementation in Aptos follows similar principles to the Ethereum implementation but is adapted to the Move language and Aptos blockchain architecture:

1. Object-based Model: Instead of ERC-20 contracts, Aptos uses an object-based model for fungible assets.

2. Scaled Balances: Like in Ethereum, the variable debt tokens use scaled balances to track user debt positions, which automatically accrue interest over time.

3. Index-based Interest Accrual: Interest accrual is handled through index-based calculations, similar to the Ethereum implementation.

4. No Transfers: Variable debt tokens cannot be transferred between users, as they represent a specific user’s debt position.

The variable debt tokens in Aave on Aptos serve the same purpose as in the Ethereum implementation: they represent a user’s variable-rate debt position in the protocol and automatically accrue interest over time based on the variable interest rate of the corresponding reserve.