Allow $type tag to be replaced by some other string (500USD Bounty)
#578
Comments
|
I'd be happy to take a stab at this @lihaoyi Is it okay if the |
|
IIRC the legacy one doesnt use a key value discriminator at all; instead, it wraps things jn two element arrays |
|
But yeah, I think in general focusing on making it work for upickle.default is fine. |
lihaoyi
pushed a commit
that referenced
this issue
May 17, 2024
Closes #578 Adds support for customizing the key used a discriminator for sealed hierarchies. The default is still `$type`, but can be customized by annotating the `sealed trait` with `@key("customKey")`. The code changes necessary to support this in `Writer` were: - Adding a new `tagKey` parameter to `TaggedWriter.Leaf` - Adding a new `TaggedWriter#findWriterWithKey` method that includes the `tagKey` in its return value - Updating `TaggedWriter#write0` to call `findWriterWithKey` and pass the `tagKey` through to `taggedWrite` - Updating `AttributeTagged#taggedWrite` to use the given `tagKey` in place of the old default key The code changes necessary to support this in `Reader` were: - Adding a new `tagKey` method to `TaggedReader`, which defaults to the old default key - Adding a `tagKey` parameter to `TaggedReader.Leaf`, `TaggedReader.Node`, `TaggedReadWriter.Leaf`, and `TaggedReadWriter.Node` to override the default value in `TaggedReader` - Updating `AttributeTagged#taggedObjectContext` to use the given `TaggedReader`'s `tagKey` in place of the old default key I tried instead to pass the `tagKey` through to `findReader`, but `findReader` is called in a number of contexts where it wasn't possible to get the `tagKey` value, for example in `TaggedReader#visitString` and the `visitValue` method within the `ObjVisitor` returned by `AttributeTagged#taggedObjectContext`. The one limitation of the customization is when a member of a sealed hierarchy inherits from multiple parents that would result in different discriminators, e.g. if two parents have `@key` annotations with different arguments, or if one parent has a `@key` annotation and another doesn't. In these cases, the macros will fail with an error telling the user what went wrong and suggesting ways to fix it: ```scala @key("customKey1") sealed trait MultiKeyedADT1 @key("customKey2") sealed trait MultiKeyedADT2 case object MultiKeyedObj extends MultiKeyedADT1 with MultiKeyedADT2 { implicit val rw: ReadWriter[MultiKeyedObj.type] = macroRW } -- Error: ---------------------------------------------------------------------- 6 | implicit val rw: ReadWriter[MultiKeyedObj.type] = macroRW | ^^^^^^^ |Type MultiKeyedObj.type inherits from multiple parent types with different discriminator keys: | | parents: MultiKeyedADT1, MultiKeyedADT2 | keys: customKey1, customKey2 | |To resolve this, either remove the `@key` annotations from all parents of the type, |or make sure all the parents pass the same value to `@key` ```
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Given a
"$type": "foo.Bar"sealed trait discriminator, Custom Keys's@keyannotation allows you to replace the right hand side"foo.Bar"of a particularcase classby annotating thecase class, but it does not allow you to replace to left hand side"$type"string with something else.This ticket is to implement the ability for a user to replace
$type"with some other string, by annotating thesealed traititself with@key("myType")annotation that would replace"$type"with"myType"for all sub-classes of thesealed trait.To incentivize contribution, I'm putting a 500USD bounty on resolving this ticket. This is payable via bank transfer, and at my discretion in case of ambiguity.
The text was updated successfully, but these errors were encountered: