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Comment by erik_seaberg | Hacker News Reader

x == y can panic if interface values contain incomparable fields in unexported nested structs, how would I check for that? Should we let it become a query of death and bet thousands of peers’ jobs on it never happening?

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Is this really the case? Can you link to anything or an example on go.dev/play/ ?

I can find a mention of "cmp.Equal" having that behavior, but that's just a third-party package panic.

It's true, but you'd never really write code like this

https://go.dev/play/p/r9NkQb6bQTx

The problem also affects structs that happen to have a private map or cache or callback anywhere within.

https://go.dev/play/p/uP-vjpvuhku

Obviously `interface{}` values are not comparable?

The comparison is explicitly allowed in the language spec, there’s no warning for doing it, and it often works depending on the types. It’s a data-dependent runtime error, which is usually hard to guarantee test coverage for.

Link to an example? I don't think this is true, unless you're playing stupid games with your code, which wouldn't pass code review.

don't do that?

this kind of thing is why deepcompare exists to begin with

It seems unrealistic to assume that everyone on a reasonably sized team knows all of the subtle edge cases to avoid and never makes mistakes

I can nag everyone to use reflect.DeepEqual and live with some false negatives, but maps always use k1 == k2.

There are also significant performance and behavior differences between the two.

They are not inter-changeable, nor can one replace the other.

more specifically, it's really strange to hear of people doing equivalence checks on objects with structure. What are you expecting that comparison to do? I doubt it is doing what you think is happening, and is indeed risky of panics.

This is days later, sorry, but - you can't use an interface as a map key, so this shouldn't apply, right?

https://go.dev/ref/spec#Map_types says that is allowed.

> If the key type is an interface type, these comparison operators must be defined for the dynamic key values; failure will cause a run-time panic.

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