Why On-Chain Loupe Functions are Good

The loupe functions are four standard functions defined by EIP-2535 Diamonds that return what functions a diamond has and the facet addresses they come from.

The verified source code of a diamond does not show what functions it has or where it gets them. And a diamond's ABI doesn't include what functions it has. To help get this information the DiamondCut event or the loupe functions are used.

The loupe functions are being used successfully by the application https://louper.dev/ to display and make diamonds transparent. It is like etherscan but for diamonds.

An important reason the loupe functions exist is because functions on smart contracts are more reliable than events. These functions make diamonds robust. This ensures their transparency and interoperability with software.

Some event systems fail, some are inconsistent and fragile. Events work better on some blockchains than others. For example on Polygon where block times are fast querying events on nodes will fail if trying to query too far back in time. Basing a system on an unreliable event system makes a system also unreliable or harder to deal with or program to make reliable. This is why diamonds use on-chain loupe functions for transparency. It is robust.

Currently the loupe functions are being used in unit tests to test diamonds. They are being used in code that deploys and upgrades diamonds. They are used by hardhat-deploy to deploy and upgrade diamonds.

It is true that DiamondCut events can be queried and processed to get the same data that the loupe functions return. This means there are two ways to get data about diamonds. Both ways can get data about diamonds and either way can be used.

So why have two ways? Because in some cases it will be easier and better to use function calls, and in other cases it will be easier and better to use events.

For example a blockchain explorer website may want to use events to show facet and function information about diamonds because it is already using event tooling and infrastructure to capture and process events for contracts.

An upgrade script may want to check that functions don't already exist in a diamond before trying to add them. Using the facets loupe function for this is simple and easy and reliable.

A simple static website can show information about any diamond by calling the loupe functions and then using the returned data to query services like Etherscan to get and show verified source code, ABI information and other information. This could be done with events, but it would be easier, simpler and probably run faster if done with loupe functions.

Having loupe functions and events give people and software choice to use what is best for their use.

There is also a question about reliability. Querying and processing events is not as reliable, available and performant as contract function calls. Likewise, a connection to an Ethereum node may not always be available in every system but there may be a connection to an events database that can be used to retrieve diamond information. Having both events and loupe functions makes diamonds robust.

The loupe functions add some complexity to diamonds. Generally it is a good idea to push complexity out of contracts into off-chain software. But every case is different and requires evaluation. In the case of diamonds there is another principle which is optimize for simplicity for common use cases. A diamond is implemented and deployed once but will be queried many times and may be used by or integrated with a lot of software. The loupe functions are a simple and direct way to query diamonds and integrate with software. The loupe functions are read-only, tested and security audited. The loupe functions can simply be added and used in every diamond without touching application specific smart contract code.

In addition the loupe functions can be deployed once and be reused by many diamonds.

Someone suggested the idea of making the loupe functions optional in the standard. The problem with that is it would break interoperability. Some diamonds would work with some software and not with other software.

I wrote another article about loupe functions that provides more information: Diamonds Loupe Functions