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• pkg/ottl: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley @edmocosta

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I wonder if we should build this into OTTL's arithmetic capabilities so you can do 9 % 2

I mentioned the Luhn algorithm specifically only because it's used as part of validation for almost all credit card schemes, but if we can reproduce the Luhn check with a math function, that would be fine. (It would be cool to have an example snippet in the docs, though.)

Although adding the reminder operator capability to OTTL would be useful, I think that wouldn't be enough for calculating the Luhn algorithm. If I'm not mistaken, it requires extra steps, such as looping through the number digits, double values, etc. which isn't supported by OTTL. That said, I'd go with a specific function Luhn(), since Mod() might be misinterpreted as normal modulus operation.

I could look into implementing this

The PR should be ready for review now - I implemented it as a specific Luhn() function now to enable the credit card checksum validation use case, but if needed, I could also follow up with another PR for a Mod() function

Hi @bixu, just to double check, do you need validating numbers using the Luhn algorithm or calculating/getting the check digit? I initially thought it was the second option, but I think I misunderstood it. If that's a validation function, I'd name it LuhnCheck, LuhnValidate or something like that.

@edmocosta, I think the most common use-case here is to check if a number is (probably) a valid CC number. So I think @bacherfl's PR will do the trick here. I agree that the function name should clearly indicate this is a bool. What about LuhnValid(<int>)?

@edmocosta, I think the most common use-case here is to check if a number is (probably) a valid CC number. So I think @bacherfl's PR will do the trick here. I agree that the function name should clearly indicate this is a bool. What about LuhnValid(<int>)?

Thanks for confirming @bixu! I think LuhnValid(<int>) would also work here. My personal preference would be LuhnCheck, but that's only my opinion (naming is hard). WDYT @TylerHelmuth @evan-bradley?

I don't have a strong opinion about the name other than signaling that the return value is a boolean. It probably makes sense to follow the style of existing functions, so I'm happy to work with whatever the maintainers decide.

Most of our boolean function start with Is such as IsRootSpan, IsMatch, IsMap, extra. To be consistent I think it would be IsValidLuhn or IsLuhnValid, IDK anything about this algorithm so IDK which is more appropriate.