| bob | withdraw(FOO, BAR, 1000) | -1000 BAR, +1000 FOO | +1000 BAR, -1000 FOO |
| alice | withdraw(BAR, FOO, 1000) | +1000 BAR, -1000 FOO | -1000 BAR, +1000 FOO |
## Publishing the contract
There are six constructor arguments.
The first three, `name`, `symbol` and `decimals` have matching getter methods, are analogous to the ERC20 methods of the same name.
The `declaration` parameter is optional and can be any arbitrary content. Typically it defines a content hash of data describing the pool resource. A value of `bytes32(0x0)` means "no declaration defined."
The `tokenRegistry` parameter takes an address to a smart contract controlling which tokens are allowed in the pool. See "Token approval" below. A value of `address(0x0)` deactivates this control, and allows the pool to hold all tokens by default (although they may still be subject to value limits).
The `tokenLimiter` parameter takes an address to a smart contract controlling value limits of tokens in the pool. See "Token limits" below. A value of `address(0x0)` deactivates this control, and allows any value of (approved) tokens to be held by the pool.
By specifying a non-zero contract address for the `tokenRegistry` property that implements the [CIC ACL](https://git.grassecon.net/cicnet/cic-contracts/#acl) interface, that contract can be used to allow and disallow which tokens can be used as input tokens to `deposit()` and `withdraw()`.
By specifying a non-zero contract address for the `tokenRegistry` property that implements the [CIC TokenLimit](https://git.grassecon.net/cicnet/cic-contracts/#tokenlimit) interface, that contract can be used to control the value limit allowed for each token in the pool.
Tokens that are limited below the current balance held by the pool can still be withdrawn. Once the balance goes below the limit, additional tokens values may again be swapped, up to the limit.
The [erc20-limiter](https://holbrook.no/src/erc20-limiter/log.html) repository contains the smart contract implementation `LimiterIndex.sol`. This uses the token limit state to satisfy the [CIC ACL](https://git.grassecon.net/cicnet/cic-contracts/#acl) interface. Specifically, any token limit higher than 0 will be defined as allowed.
This enables to publisher to use the same smart contract for both constructor arguments `tokenRegistry` and `tokenLimiter`.
## Handling values
The pool contract does no checking whatsoever regarding the sanity of allowing tokens in the pool.
It is therefore the responsibility of the maintainer of the list of allowed tokens to ensure that tokens in the pool are exchangeable in a sensible way.
Some obvious concerns are:
- Tokens are swapped denominated in their smallest unit (regardless of "decimals").
- The unit of account of the tokens may differ.
- The value of the tokens in relation to unit of account may differ.
An example quoter contract `DecimalQuote.sol` can be found in this repository. The contract translates values according to the decimal count reported by the respective ERC20 tokens.
## Fees
Using the `setFee` method, a fee may be specified, in parts-per-million, to be deducted from each token swap.
The fee will be deducted from the input token _before_ the value is sent to the "quoter" (if defined).
Fee is defined in _parts-per-million_, i.e. `1000000` equals `100%`. Any value less than 1000000 is value.
### Fee recipient
By default, all deducted fees are credited to the pool contract.
Using the `setFeeAddress` method, an external beneficiary for the fees may be defined. That beneficiary will receive all fees _from that moment on_.
Fees to be paid externally are accounted for internally in the contract, and may be withdrawn at any time using either the `withdraw(outToken)` or `withdraw(outToken, value)` method. (Note the difference in method signature from the exchange method: `withdraw(outToken, inToken, value)`.
