Custom type as a Mapper + Receiver

[Vivek Shankar]

I am trying to create a custom type with all the capabilities of a mapper, such as indexing and iteration, but with some additional function overloads. This doesn't seem to work and I get the "no such overload" error, probably because the "." operator looks for a field instead of calling into the receiver, but I wanted to confirm there is no way to do this.

The following is my custom type.

type User struct {

    ref.TypeAdapter

    context *vctx.VerifyContext

    m map[string]interface{}

    traits.Mapper

    traits.Receiver

}

var (

    UserType = types.NewTypeValue("User",

         traits.ContainerType,

         traits.IndexerType,

         traits.IterableType,

         traits.SizerType,

         traits.ReceiverType)

)

In the constructor func, it just creates a new dynamic map (types.NewDynamicMap) and passes in the source map[string]interface{} into it. This is assigned to Mapper in the struct instance. So basically the struct hands off all mapper logic to the underlying Mapper instance.

Thanks for your help.

[Vivek Shankar]

My mistake. I did not override the Type() and so it was picking up the type that baseMap returns.

[Espen Zachrisen]

I implemented support for native Go structs if you're interested in the code. 

Here are tests showing how it works: https://github.com/ezachrisen/indigo/blob/master/cel/examples/examples_test.go.

This is in the "experimental" state, but would love to collaborate if you're interested. 

-- Espen 

[Tristan Swadell]

Hi Espen,

I definitely think that it would be good to provide a GoTypeProvider as an alternative to proto for adding custom types to CEL. I more or less created an OpenAPISchema type provider for CEL Policy Templates, so I'm happy to see similarities between your implementation and my own since it speaks to how well the existing interfaces can be used to augment the type systems supported within CEL. 

-Tristan 

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[Espen Zachrisen]

Yes, I agree, I found the interfaces easy to work with. (Having said that, if you see anything in my code that isn't right, let me know!) I used the Istio example you've mentioned before as a reference. 

It's pretty remarkable that CEL can be extended in this way. I know that flexibility doesn't happen by accident - kudos to whoever designed it! 

-- Espen

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[Vivek Shankar]

Hi Espen,

This looks really useful. I implemented my custom types using the TypeAdapter approach. I am unsure when I should be using one over the other but this your AttributeProvider appears to be the way to go as the number of custom types grow?

Thanks for sharing this.

Cheers,

Vivek