TLDR; What should I emit for inspect/2 output of library structs? Executable code, string representation or default (outputs the struct fields)? Summary In April, I changed the output of inspect/2 for Cldr.LanguageTag.t to be executable code rather than the default structural output. I did this to…

I expect executable code as a result of inspect. In my projects, I also change it to this effect. If I want to see the structure I use: iex> Date.utc_today() ~D[2024-07-03] iex> Date.utc_today() |> inspect(structs: false) "%{calendar: Calendar.ISO, month: 7, __struct__: Date, day: 3, year: 2024}"

To me “exectuable code” inspection format is a (better) alternative to the previous convention of having #Struct.Name<…> format. But I don’t expect it in places where no custom inspect implementation is needed and/or makes sense, so I don’t consider that new pattern a general one to be applied every…

The standard library is not a great example because Date, Time, Regex, Range, etc, all have built-in sigils and operators, imported by default, which are compact and justify using the same notation for printing them. If we remove those from the equation, we end-up with: URI, File.Stream, Version -…

@josevalim This is a very useful breakdown and I’m glad the original question was asked. Would this make sense in the documentation somewhere? Maybe under Library Guidelines ?

I think that’d be appropriate

[image] josevalim: If no, is there an executable version? José, thank you, I think these are a good addition to the inspect/2 docs. I’m probably overthinking it again but I’m not able to reconcile the “If yes (expose the struct without leaking implementation details), then output the struct”…

[image] kip: Those don’t appear to include implementation details and yet they output executable code - albeit in sigil form. This seems to be what makes them exceptions, but also aren’t structs just as executable as sigils? I’m a bit confused by that category. I can definitely see the advant…

I don’t see the downsides to emitting structs when they are public Thats definitely part of my consideration here. There is an argument (going on in my head) about whether Cldr.LanguageTag.t should be opaque. In which case the inspect output would not be the structure. I don’t see the downsides…

[image] tfwright: On the other hand it’s not clear to me why MapSet returns what it does so it’s likely I’m missing something. MapSet is an opaque type. It means the internal representation might change at any time – even has in the past, so not just a theoretical thing. Therefore it cannot s…

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Inspect/2 output for structs: executable code or structure?

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josevalim July 4, 2024, 6:20am 6

Perhaps we could document it under Inspect itself?