maybe search lexical scope for substitutions? (was: list entry local variable resolution) about config

[mmuschalik]

Another suggestion is the following:

Local scope:
^{this.name}

Parent scope:
^{super.name}

Global scope:
${name}

So, adopt the Java way of class inheritance, but obviously keep backwards compatibility.

[havocp]

substitutions are "global", so ${some-id} refers to some-id at the root. There's no way to do substitutions that refer to list elements.

yes, I got that; what I meant - do you think there is an extension on hocon rules that would permit this?

[havocp]

Two quick ideas would be:

• if we don't resolve globally, we try "lexical scope" search or "only in the same object" search
• an alternative syntax like ^{some-id} or something

I guess the first would be a little more in the "figure out what you meant" spirit of HOCON.

It might be some effort to implement; right now objects don't have a parent reference (and adding parent references could add a lot of object copying). So some kind of parent chain might have to be built when traversing the tree to resolve substitutions and then that chain would have to be passed in to the substitution-resolver code. (Just speculating here really, I may not remember the code properly. The point is it might be kind of tricky to implement.)

It's likely surprising that global search would be before lexical/local search, but it would have to be that way to be backward compatible.

re: "if we don't resolve globally, we try "lexical scope" search or "only in the same object" search" - I like this

on a related note, do you have v 1.0.0 closer on your horizon?

[havocp]

1.0.0 is basically just supposed to be timed with the next Scala/Akka release - which is "soon" afaik.

[jsuereth]

1-2 weeks before RC1

[fehmicansaglam]

What is the current situation for this issue? Do you have to plan to support "lexical scope"?

[havocp]

I don't have any immediate plan. It's just a discussion that has come up / can be discussed further, if people have thoughts.

[fehmicansaglam]

I see. I want to ask a question. I am trying to add Fixtures support to ReactiveMongo Extensions. Defining fixtures by HOCON seems to be a good idea. But as there is no locality in substitutions it is somewhat cumbersome to specify references. Currently it is not possible to do this:

_collection.persons {

    person1 {
        _id: _id_person1
        name: Ali
        surname: Veli
        fullname: ${name} ${surname}
        age: 32
    }

    person2 {
        _id: _id_person2
        name: Haydar
        surname: Cabbar
        fullname: ${name} ${surname}
        age: ${person1.age}
    }
}

Ability to inject a custom resolver would be great.

[havocp]

If you are up to implementing a custom resolve I think you could do that now with Config.resolveWith() and ConfigResolveOptions.setAllowUnresolved() - traverse the tree building the lexical stack and then resolveWith each node in the stack until resolution is complete. I guess the API is there but it would be a lot of code to write.

For a built-in lexical scope feature there's some work just to figure out how to spec it and how it should work, with a focus on usability, and then of course the work to implement it. I don't have an immediate plan to do either part of the work but if someone's passionate and wants to dig in I can try to help.

Syntax ideas:

• ^{look.up.lexically}
• ${^look.up.lexically}
• ${.look.up.lexically}

? not sure really. I haven't even checked that ^ is one of the reserved chars that we could use (spec has a list).

[fehmicansaglam]

Thanks for your help. I have implemented scopes using resolveWith. And with not that much code.

[bmarwell]

Hello. This issue is pretty old, but still needed. Are you going to put any effort into it?

[havocp]

I don’t have plans to work on this, but of course others are welcome to.

[jvanzyl]

@fehmicansaglam Might you be able to share your code for lexically scoped substitutions?

[fehmicansaglam]

@jvanzyl it's been too long time but here's the code: https://github.com/fehmicansaglam/reactivemongo-extensions/blob/0.10.x/core/src/main/scala/fixtures/Fixtures.scala

[jvanzyl]

Thanks so much!