I’ve been playing with dhall-kubernetes a bit recently, and I’m finding myself repeating the same snippet of code:
let myDeployment -- Deployment is an example, it could be any kubernetes type really
: types.Deployment
= defaults.Deployment
⫽ { metadata =
defaults.ObjectMeta
⫽ { namespace =
Some "default"
, name =
"prometheus-operator"
, labels =
./commonLabels.dhall
}
-- ...
Basically, I want to override the default values of metadata.name, metadata.namespace and metadata.labels. In order to do this, I need to reference defaults.ObjectMeta (or possibly defaults.Deployment.metadata) to get the rest of the metadata fields, which i don’t want to change.
It feels clunky to have to reference the defaults for the metadata field when I have already set defaults for the whole data structure. When using ⫽, I can’t skip defaults.ObjectMeta because ⫽ is non-recursive and will replace the whole record. I thought I could try ∧ instead, which is recursive, but it doesn’t allow replacing fields which already exist (in this example, I can use ∧ to set name but not namespace or labels, which have defaults.)
In other languages, I’m used to being able to update a single value within a nested data structure without so much wrangling. For example, Clojure’s assoc-in function allows you to upsert a value at an arbitrary path in a nested data structure. (side note: it even plays nicely if some of the nested layers are vectors rather than maps)
It feels like there could be a recursive variant of ⫽ which might meet my needs (though I can see that specifying its behaviour might be tricky). Is this something which has previously been considered and rejected? It would look something like this:
let myDeployment -- Deployment is an example, it could be any kubernetes type really
: types.Deployment
= defaults.Deployment
/// { metadata =
{ namespace =
Some "default"
, name =
"prometheus-operator"
, labels =
./commonLabels.dhall
}
-- ...