The usage of the ensure(condition, build_CUSTOM_ERROR(CUSTOM_ERROR parameters)) function is considered to be Gas-inefficient compared to require(condition, "Error message") and if (!condition) revert CUSTOM_ERROR(CUSTOM_ERROR parameters).
Starting from solidity 0.8.4, Custom Errors are available, providing the ability to efficiently return dynamic data packed in an efficient format.
However, the previously used validation pattern with the require function does not have support for Custom Errors. In this way, the validation style changed significantly, and the declarativeness of the require pattern was missed.
In smart contracts, it is often more valuable to check if values are within certain bounds rather than out of bounds. The require pattern allowed for this perfectly, while the revert pattern made the code look more branchy, decreasing readability.
This project aims to develop an ensure function that allows the usage of Custom Errors within a declarative require pattern.
Custom Errors are ABI encoded as follows:
- 4 bytes Custom Error selector
- 32 bytes for each Custom Error parameter
It was decided to use abi.encode to pack Custom Error parameters into 32 bytes memory slots. After evaluating efficiency, abi.encode(uint32(selector), parameters) was found to be more optimal than abi.encodePacked(selector, abi.encode(parameters)), hence the prior was chosen.
To throw the error message, the assembly revert instruction is used, allowing for starting the error message from any memory pointer and directly providing the message length.
It is worth mentioning that abi.encode accepts parameters of any type, which led to the proposal of building builder functions for each error. These builder functions accept corresponding parameters and perform auto typechecks.
The ensure function has been developed and should be used within the ensure(condition, build_CUSTOM_ERROR(CUSTOM_ERROR parameters)) pattern. It preserves the declarative require pattern and allows for the usage of Custom Errors.
Refer to the Example.sol file for an implementation example.
However, there are some flaws:
- The need to declare a builder function for each error leads to code overload and increased Gas consumption during deployment.
- Custom Error data is not lazily built, and the error message is calculated before the function call, causing ordinary checks to incur additional Gas costs based on the error parameter types.
I have raised an issue in the ethereum/solidity repo to address the lack of Custom Errors support in the require function.