Curve Token V3
The Curve Token V3 is more gas efficient than versions 1 and 2. The implementation for a Curve Token V3 may be viewed on GitHub.
Note
Compared to the Curve Token V2 API, there have been the following changes:
increaseAllowance and decreaseAllowance methods added to mitigate race conditions.
CurveToken.increaseAllowance¶
CurveToken.increaseAllowance(_spender: address, _added_value: uint256) → bool
Increase the allowance granted to _spender by the msg.sender.
This is alternative to approve that can be used as a mitigation for the potential race condition. Returns True if success.
| Input | Type | Description |
|---|---|---|
_spender | address | Account whose tokens will be burned |
_value | uint256 | Amount that will be burned |
Emits: Approval
Source code
@external
def approve(_spender : address, _value : uint256) -> bool:
"""
@notice Approve the passed address to transfer the specified amount of
tokens on behalf of msg.sender
@dev Beware that changing an allowance via this method brings the risk
that someone may use both the old and new allowance by unfortunate
transaction ordering. This may be mitigated with the use of
{increaseAllowance} and {decreaseAllowance}.
https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
@param _spender The address which will transfer the funds
@param _value The amount of tokens that may be transferred
@return bool success
"""
self.allowance[msg.sender][_spender] = _value
log Approval(msg.sender, _spender, _value)
return True
@external
def increaseAllowance(_spender: address, _added_value: uint256) -> bool:
"""
@notice Increase the allowance granted to `_spender` by the caller
@dev This is alternative to {approve} that can be used as a mitigation for
the potential race condition
@param _spender The address which will transfer the funds
@param _added_value The amount of to increase the allowance
@return bool success
"""
allowance: uint256 = self.allowance[msg.sender][_spender] + _added_value
self.allowance[msg.sender][_spender] = allowance
log Approval(msg.sender, _spender, allowance)
return True
CurveToken.decreaseAllowance¶
CurveToken.decreaseAllowance(_spender: address, _subtracted_value: uint256) → bool
Decrease the allowance granted to _spender by the msg.sender.
This is alternative to approve that can be used as a mitigation for the potential race condition. Returns True if success.
| Input | Type | Description |
|---|---|---|
_spender | address | Account whose tokens will be burned |
_added_value | uint256 | Amount that will be burned |
Emits: Approval
Source code
@external
def approve(_spender : address, _value : uint256) -> bool:
"""
@notice Approve the passed address to transfer the specified amount of
tokens on behalf of msg.sender
@dev Beware that changing an allowance via this method brings the risk
that someone may use both the old and new allowance by unfortunate
transaction ordering. This may be mitigated with the use of
{increaseAllowance} and {decreaseAllowance}.
https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
@param _spender The address which will transfer the funds
@param _value The amount of tokens that may be transferred
@return bool success
"""
self.allowance[msg.sender][_spender] = _value
log Approval(msg.sender, _spender, _value)
return True
@external
def decreaseAllowance(_spender: address, _subtracted_value: uint256) -> bool:
"""
@notice Decrease the allowance granted to `_spender` by the caller
@dev This is alternative to {approve} that can be used as a mitigation for
the potential race condition
@param _spender The address which will transfer the funds
@param _subtracted_value The amount of to decrease the allowance
@return bool success
"""
allowance: uint256 = self.allowance[msg.sender][_spender] - _subtracted_value
self.allowance[msg.sender][_spender] = allowance
log Approval(msg.sender, _spender, allowance)
return True