Last update: October 8, 2021

BaseStrategy

Functions

apiVersion

  function apiVersion(
  ) public returns (string)

@notice Used to track which version of StrategyAPI this Strategy implements.

The Strategy’s version must match the Vault’s API_VERSION.

Return Values:

Name	Type	Description
`A`		string which holds the current API version of this contract.
### name
`function name( ) external returns (string)`
This Strategy’s name.
@dev
You can use this field to manage the “version” of this Strategy, e.g.
`StrategySomethingOrOtherV1`. However, “API Version” is managed by
`apiVersion()` function above.

Return Values:

Name	Type	Description
`This`		Strategy’s name.
### delegatedAssets
`function delegatedAssets( ) external returns (uint256)`
@notice
The amount (priced in want) of the total assets managed by this strategy should not count
towards Yearn’s TVL calculations.
@dev
You can override this field to set it to a non-zero value if some of the assets of this
Strategy is somehow delegated inside another part of of Yearn’s ecosystem e.g. another Vault.
Note that this value must be strictly less than or equal to the amount provided by
`estimatedTotalAssets()` below, as the TVL calc will be total assets minus delegated assets.
Also note that this value is used to determine the total assets under management by this
strategy, for the purposes of computing the management fee in `Vault`
@return
The amount of assets this strategy manages that should not be included in Yearn’s Total Value
Locked (TVL) calculation across it’s ecosystem.

_onlyAuthorized

  function _onlyAuthorized(
  ) internal

_onlyEmergencyAuthorized

  function _onlyEmergencyAuthorized(
  ) internal

_onlyStrategist

  function _onlyStrategist(
  ) internal

_onlyGovernance

  function _onlyGovernance(
  ) internal

_onlyKeepers

  function _onlyKeepers(
  ) internal

constructor

  function constructor(
  ) public

_initialize

  function _initialize(
    address _vault,
    address _strategist,
    address _rewards,
    address _keeper
  ) internal

@notice Initializes the Strategy, this is called only once, when the contract is deployed.

_vault should implement VaultAPI.

Parameters:

Name	Type	Description
`_vault`	address	The address of the Vault responsible for this Strategy.
`_strategist`	address	The address to assign as `strategist`.
The strategist is able to change the reward address
`_rewards`	address	The address to use for pulling rewards.
`_keeper`	address	The adddress of the _keeper. _keeper
can harvest and tend a strategy.

setStrategist

  function setStrategist(
    address _strategist
  ) external

@notice Used to change strategist.

This may only be called by governance or the existing strategist.

Parameters:

Name	Type	Description
`_strategist`	address	The new address to assign as `strategist`.

setKeeper

  function setKeeper(
    address _keeper
  ) external

@notice Used to change keeper.

keeper is the only address that may call tend() or harvest(), other than governance() or strategist. However, unlike governance() or strategist, keeper may only call tend() and harvest(), and no other authorized functions, following the principle of least privilege.

This may only be called by governance or the strategist.

Parameters:

Name	Type	Description
`_keeper`	address	The new address to assign as `keeper`.

setRewards

  function setRewards(
    address _rewards
  ) external

@notice Used to change rewards. EOA or smart contract which has the permission to pull rewards from the vault.

This may only be called by the strategist.

Parameters:

Name	Type	Description
`_rewards`	address	The address to use for pulling rewards.

setMinReportDelay

  function setMinReportDelay(
    uint256 _delay
  ) external

@notice Used to change minReportDelay. minReportDelay is the minimum number of blocks that should pass for harvest() to be called.

For external keepers (such as the Keep3r network), this is the minimum time between jobs to wait. (see harvestTrigger() for more details.)

This may only be called by governance or the strategist.

Parameters:

Name	Type	Description
`_delay`	uint256	The minimum number of seconds to wait between harvests.

setMaxReportDelay

  function setMaxReportDelay(
    uint256 _delay
  ) external

@notice Used to change maxReportDelay. maxReportDelay is the maximum number of blocks that should pass for harvest() to be called.

For external keepers (such as the Keep3r network), this is the maximum time between jobs to wait. (see harvestTrigger() for more details.)

This may only be called by governance or the strategist.

Parameters:

Name	Type	Description
`_delay`	uint256	The maximum number of seconds to wait between harvests.

setProfitFactor

  function setProfitFactor(
    uint256 _profitFactor
  ) external

@notice Used to change profitFactor. profitFactor is used to determine if it’s worthwhile to harvest, given gas costs. (See harvestTrigger() for more details.)

This may only be called by governance or the strategist.

Parameters:

Name	Type	Description
`_profitFactor`	uint256	A ratio to multiply anticipated
`harvest()` gas cost against.

setDebtThreshold

  function setDebtThreshold(
    uint256 _debtThreshold
  ) external

@notice Sets how far the Strategy can go into loss without a harvest and report being required.

By default this is 0, meaning any losses would cause a harvest which will subsequently report the loss to the Vault for tracking. (See harvestTrigger() for more details.)

This may only be called by governance or the strategist.

Parameters:

Name	Type	Description
`_debtThreshold`	uint256	How big of a loss this Strategy may carry without
being required to report to the Vault.

setMetadataURI

  function setMetadataURI(
    string _metadataURI
  ) external

@notice Used to change metadataURI. metadataURI is used to store the URI of the file describing the strategy.

This may only be called by governance or the strategist.

Parameters:

Name	Type	Description
`_metadataURI`	string	The URI that describe the strategy.

governance

  function governance(
  ) internal returns (address)

Resolve governance address from Vault contract, used to make assertions on protected functions in the Strategy.

ethToWant

  function ethToWant(
    uint256 _amtInWei
  ) public returns (uint256)

@notice Provide an accurate conversion from _amtInWei (denominated in wei) to want (using the native decimal characteristics of want). @dev Care must be taken when working with decimals to assure that the conversion is compatible. As an example:

 given 1e17 wei (0.1 ETH) as input, and want is USDC (6 decimals),
 with USDC/ETH = 1800, this should give back 180000000 (180 USDC)

Parameters:

Name	Type	Description
`_amtInWei`	uint256	The amount (in wei/1e-18 ETH) to convert to `want`

Return Values:

Name	Type	Description
`The`	uint256	amount in `want` of `_amtInEth` converted to `want`

estimatedTotalAssets

  function estimatedTotalAssets(
  ) public returns (uint256)

@notice Provide an accurate estimate for the total amount of assets (principle + return) that this Strategy is currently managing, denominated in terms of want tokens.

This total should be “realizable” e.g. the total value that could actually be obtained from this Strategy if it were to divest its entire position based on current on-chain conditions. @dev Care must be taken in using this function, since it relies on external systems, which could be manipulated by the attacker to give an inflated (or reduced) value produced by this function, based on current on-chain conditions (e.g. this function is possible to influence through flashloan attacks, oracle manipulations, or other DeFi attack mechanisms).

It is up to governance to use this function to correctly order this Strategy relative to its peers in the withdrawal queue to minimize losses for the Vault based on sudden withdrawals. This value should be higher than the total debt of the Strategy and higher than its expected value to be “safe”.

Return Values:

Name	Type	Description
`The`		estimated total assets in this Strategy.
### isActive
`function isActive( ) public returns (bool)`

prepareReturn

  function prepareReturn(
  ) internal returns (uint256 _profit, uint256 _loss, uint256 _debtPayment)

Perform any Strategy unwinding or other calls necessary to capture the “free return” this Strategy has generated since the last time its core position(s) were adjusted. Examples include unwrapping extra rewards. This call is only used during “normal operation” of a Strategy, and should be optimized to minimize losses as much as possible.

This method returns any realized profits and/or realized losses incurred, and should return the total amounts of profits/losses/debt payments (in want tokens) for the Vault’s accounting (e.g. want.balanceOf(this) >= _debtPayment + _profit).

_debtOutstanding will be 0 if the Strategy is not past the configured debt limit, otherwise its value will be how far past the debt limit the Strategy is. The Strategy’s debt limit is configured in the Vault.

NOTE: _debtPayment should be less than or equal to _debtOutstanding. It is okay for it to be less than _debtOutstanding, as that should only used as a guide for how much is left to pay back. Payments should be made to minimize loss from slippage, debt, withdrawal fees, etc.

See vault.debtOutstanding().

adjustPosition

  function adjustPosition(
  ) internal

Perform any adjustments to the core position(s) of this Strategy given what change the Vault made in the “investable capital” available to the Strategy. Note that all “free capital” in the Strategy after the report was made is available for reinvestment. Also note that this number could be 0, and you should handle that scenario accordingly.

See comments regarding _debtOutstanding on prepareReturn().

liquidatePosition

  function liquidatePosition(
  ) internal returns (uint256 _liquidatedAmount, uint256 _loss)

Liquidate up to _amountNeeded of want of this strategy’s positions, irregardless of slippage. Any excess will be re-invested with adjustPosition(). This function should return the amount of want tokens made available by the liquidation. If there is a difference between them, _loss indicates whether the difference is due to a realized loss, or if there is some other sitution at play (e.g. locked funds) where the amount made available is less than what is needed.

NOTE: The invariant _liquidatedAmount + _loss <= _amountNeeded should always be maintained

liquidateAllPositions

  function liquidateAllPositions(
  ) internal returns (uint256 _amountFreed)

Liquidate everything and returns the amount that got freed. This function is used during emergency exit instead of prepareReturn() to liquidate all of the Strategy’s positions back to the Vault.

tendTrigger

  function tendTrigger(
    uint256 callCostInWei
  ) public returns (bool)

@notice Provide a signal to the keeper that tend() should be called. The keeper will provide the estimated gas cost that they would pay to call tend(), and this function should use that estimate to make a determination if calling it is “worth it” for the keeper. This is not the only consideration into issuing this trigger, for example if the position would be negatively affected if tend() is not called shortly, then this can return true even if the keeper might be “at a loss” (keepers are always reimbursed by Yearn). @dev callCostInWei must be priced in terms of wei (1e-18 ETH).

This call and harvestTrigger() should never return true at the same time.

Parameters:

Name	Type	Description
`callCostInWei`	uint256	The keeper’s estimated gas cost to call `tend()` (in wei).

Return Values:

Name	Type	Description
`if`	uint256	`tend()` should be called, `false` otherwise.
### tend
`function tend( ) external`
@notice
Adjust the Strategy’s position. The purpose of tending isn’t to
realize gains, but to maximize yield by reinvesting any returns.

See comments on adjustPosition().

This may only be called by governance, the strategist, or the keeper.

harvestTrigger

  function harvestTrigger(
    uint256 callCostInWei
  ) public returns (bool)

@notice Provide a signal to the keeper that harvest() should be called. The keeper will provide the estimated gas cost that they would pay to call harvest(), and this function should use that estimate to make a determination if calling it is “worth it” for the keeper. This is not the only consideration into issuing this trigger, for example if the position would be negatively affected if harvest() is not called shortly, then this can return true even if the keeper might be “at a loss” (keepers are always reimbursed by Yearn). @dev callCostInWei must be priced in terms of wei (1e-18 ETH).

This call and tendTrigger should never return true at the same time.

See min/maxReportDelay, profitFactor, debtThreshold to adjust the strategist-controlled parameters that will influence whether this call returns true or not. These parameters will be used in conjunction with the parameters reported to the Vault (see params) to determine if calling harvest() is merited.

It is expected that an external system will check harvestTrigger(). This could be a script run off a desktop or cloud bot (e.g. https://github.com/iearn-finance/yearn-vaults/blob/main/scripts/keep.py), or via an integration with the Keep3r network (e.g. https://github.com/Macarse/GenericKeep3rV2/blob/master/contracts/keep3r/GenericKeep3rV2.sol).

Parameters:

Name	Type	Description
`callCostInWei`	uint256	The keeper’s estimated gas cost to call `harvest()` (in wei).

Return Values:

Name	Type	Description
`if`	uint256	`harvest()` should be called, `false` otherwise.
### harvest
`function harvest( ) external`
@notice
Harvests the Strategy, recognizing any profits or losses and adjusting
the Strategy’s position.

In the rare case the Strategy is in emergency shutdown, this will exit the Strategy’s position.

This may only be called by governance, the strategist, or the keeper. @dev When harvest() is called, the Strategy reports to the Vault (via vault.report()), so in some cases harvest() must be called in order to take in profits, to borrow newly available funds from the Vault, or otherwise adjust its position. In other cases harvest() must be called to report to the Vault on the Strategy’s position, especially if any losses have occurred.

withdraw

  function withdraw(
    uint256 _amountNeeded
  ) external returns (uint256 _loss)

@notice Withdraws _amountNeeded to vault.

This may only be called by the Vault.

Parameters:

Name	Type	Description
`_amountNeeded`	uint256	How much `want` to withdraw.

Return Values:

Name	Type	Description
`_loss`	uint256	Any realized losses
### prepareMigration
`function prepareMigration( ) internal`
Do anything necessary to prepare this Strategy for migration, such as
transferring any reserve or LP tokens, CDPs, or other tokens or stores of
value.

migrate

  function migrate(
    address _newStrategy
  ) external

@notice Transfers all want from this Strategy to _newStrategy.

This may only be called by the Vault. @dev The new Strategy’s Vault must be the same as this Strategy’s Vault. The migration process should be carefully performed to make sure all the assets are migrated to the new address, which should have never interacted with the vault before.

Parameters:

Name	Type	Description
`_newStrategy`	address	The Strategy to migrate to.

setEmergencyExit

  function setEmergencyExit(
  ) external

@notice Activates emergency exit. Once activated, the Strategy will exit its position upon the next harvest, depositing all funds into the Vault as quickly as is reasonable given on-chain conditions.

This may only be called by governance or the strategist. @dev See vault.setEmergencyShutdown() and harvest() for further details.

protectedTokens

  function protectedTokens(
  ) internal returns (address[])

Override this to add all tokens/tokenized positions this contract manages on a persistent basis (e.g. not just for swapping back to want ephemerally).

NOTE: Do not include want, already included in sweep below.

Example:

   function protectedTokens() internal override view returns (address[] memory) {
     address[] memory protected = new address[](3);
     protected[0] = tokenA;
     protected[1] = tokenB;
     protected[2] = tokenC;
     return protected;
   }

sweep

  function sweep(
    address _token
  ) external

@notice Removes tokens from this Strategy that are not the type of tokens managed by this Strategy. This may be used in case of accidentally sending the wrong kind of token to this Strategy.

Tokens will be sent to governance().

This will fail if an attempt is made to sweep want, or any tokens that are protected by this Strategy.

This may only be called by governance. @dev Implement protectedTokens() to specify any additional tokens that should be protected from sweeping in addition to want.

Parameters:

Name	Type	Description
`_token`	address	The token to transfer out of this vault.

Events

Harvested

  event Harvested(
  )

UpdatedStrategist

  event UpdatedStrategist(
  )

UpdatedKeeper

  event UpdatedKeeper(
  )

UpdatedRewards

  event UpdatedRewards(
  )

UpdatedMinReportDelay

  event UpdatedMinReportDelay(
  )

UpdatedMaxReportDelay

  event UpdatedMaxReportDelay(
  )

UpdatedProfitFactor

  event UpdatedProfitFactor(
  )

UpdatedDebtThreshold

  event UpdatedDebtThreshold(
  )

EmergencyExitEnabled

  event EmergencyExitEnabled(
  )

UpdatedMetadataURI

  event UpdatedMetadataURI(
  )