GEB Docs
Token Adapters
The gateways for collateral and system coins to join or exit the system

1. Summary

There are three main token adapter types: CollateralJoin, ETHJoin and CoinJoin:
  • CollateralJoin - allows standard ERC20 tokens to be deposited for use with the system.
  • ETHJoin - allows native Ether to be used with the system.
  • CoinJoin - allows users to withdraw their system coins from the protocol into a standard ERC20 token (and vice-versa).

2. Contract Variables & Functions

  • safeEngine - storage of the SAFEEngine’s address.
  • collateralType - id of the CollateralType for which a CollateralJoin is created for.
  • collateral - the address of the collateralType for transferring.
  • systemCoin - the address of the Coin token.
  • contractEnabled - an access flag for the adapter.
  • decimals - decimals for the collateral type.
  • join - join tokens into the system
  • exit - exit tokens from the system
  • disableContract - disable the adapter and only allow exits

3. Walkthrough

All adapter contracts serve a similar purpose. They manage the flow of collateral and system coins in and out of the system using join and exit. CollateralJoin is meant to change the SAFEEngine.tokenCollateral and CoinJoin changes SAFEEngine.coinBalances.
CoinJoin Can Be Used to Upgrade the ERC20 System Coin
CoinJoin is a gateway (like an ATM) between the SAFEEngine and the ERC20 representation of the system coin (cash). Governance has the power to deploy multiple CoinJoins and disable previous Join contracts. When a CoinJoin is disabled, users can only burn ERC20 system coins for SAFEEngine.coinBalance (join coins into the system) and can no longer exit their SAFEEngine.coinBalance in the ERC20 (thus, the "gateway" only allows for one way transfers).
If governance wants, they can deploy another ERC20 Coin contract (possibly with blacklisting capabilities) and also a separate CoinJoin for this new token. The previous CoinJoin for the old Coin contract can be disabled so that old ERC20 tokens can only be joined in the system. The process to upgrade between the old, permissionless Coin and the new, permissioned one can be extremely complicated (although not impossible) because some coin holders may not want to do the switch.