increaseAllowancedecreaseAllowance

IncreaseAllowance and decreaseAllowance are commonly used helper functions in the ERC-20 token standard that manage how much a designated spender is allowed to spend on behalf of the token holder. They provide a relative way to adjust an existing allowance, rather than setting a new absolute value directly, which can help reduce certain approval-related risks.

Function and behavior overview: increaseAllowance(address spender, uint256 addedValue) increases the current allowance for the specified spender by addedValue, typically calling an internal approve function to set the new total. decreaseAllowance(address spender, uint256 subtractedValue) reduces the current allowance by subtractedValue, and it typically caps at zero to avoid negative allowances. These wrappers are designed to be simple, returning true on success and relying on the contract’s standard approval flow.

Rationale and usage: The standard approve pattern in ERC-20 can lead to race conditions if a spender acts between the prior approval and a new one. Using increaseAllowance and decreaseAllowance helps manage changes incrementally, reducing the likelihood of overspending due to timing. They are especially helpful when a token holder routinely adjusts allowances for trusted contractors or decentralized applications.

Implementation and compatibility: These functions are optional helpers in the ERC-20 interface. Some tokens implement them, often following common libraries such as OpenZeppelin’s ERC-20 extension. Not all tokens support or expose them, so developers should verify token contract documentation before relying on these methods.

Security and considerations: While they mitigate certain race conditions, increaseAllowance and decreaseAllowance do not eliminate all risks associated with allowances. Moreover, users should still follow best practices, such as approving zero before changing to a new value in some scenarios, depending on the token contract’s specifics.