except vs private ?

[lloydtabb]

I'm not sure we have the concept of 'except' right. Consider:

source: a is airports extend {
  where: state='CA'
} extend {
  except: state
}

run: a -> {select: *}

Right now we blow up. The goal here is to use state to perform a filter but not have it available on subsequent sources. Do we want something like private instead?

[christopherswenson]

Yeah, currently all except does is delete state from the fields, which doesn't work if you have a filter using that field... except came from a time when we didn't really expect you to extend a source multiple times.

It does seem like instead of removing it outright we could just mark it as inaccessible, which I think would solve this issue. @mtoy-googly-moogly

[christopherswenson]

Renaming except to private is an interesting idea, but we do have the same issue with accept:

source: a1 is airports extend {
  where: state='CA'
} extend {
  accept: code
}
run: a1 -> {select: *}

We should consider a new strategy for limiting fields...

source: a1 is airports extend {
  where: state='CA'
} extend {
  private: state // makes an existing field private
  private dimension: my_field is ... // make a new field which is private

  // also probably need some form of "accept"... maybe something like
  private: * { except: state }
  // or perhaps we just keep
  accept: state // to mean make everything except state private
  
  // only semi-related, but add tags to an inherited field
  dimension: 
    # new_tag
    my_field
}

[mtoy-googly-moogly]

except/accept are filters and the are processed super early in the construction of a source, and they are implemented using the same mechanism, so lloyd's hope that this would be quick or easy is dashed.

it was also just a quick hack, i knew that editing the namespace would someday be important, but we didn't really know enough to do much so it is kind of a placeholder for namespace management. it isn't a beautiful and prefect design.

There is a discussion brewing on namespace management, this should get folded into that. I could see that when we are done and have public/protected/private accept/except could become a deprecated feature which was implemented by filtering with private instead of removal