Was also wondering if there could be a `foo validate ` using optics to return an `Either lt Nel lt ValidationError gt Foo gt ` for validating data class hierarchies after they were deserialized

```val foo = Foo val result Either lt ValidationError Foo gt = foo validate Foo baz eq 20 Foo bar bara barb eq something ```

Was also wondering if there could be a `foo validate ` using kotlinlang #arrow

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dave08

03/01/2023, 1:40 PM

Was also wondering if there could be a

foo.validate { }

using optics to return an

Either<Nel<ValidationError>, Foo>

for validating data class hierarchies after they were deserialized...?

It could be used when

ensure

and

zipOrAccumulate

can't be used, because object instantiation isn't in the app code's control...

Alejandro Serrano Mena

03/01/2023, 1:53 PM

how would you envision it working?

dave08

03/01/2023, 1:56 PM

val foo = Foo(...)

val result: Either<ValidationError, Foo> = foo.validate {
   Foo.baz eq 20
   Foo.bar.bara.barb eq "something"
 }

Each line that doesn't pass could be accumulated in the Left.

And if they all pass, Right is returned with Foo

Does this make any sense @Alejandro Serrano Mena? It's you that had the great idea to add

copy { }

... I just thought to use the same pattern for validation...!

Alejandro Serrano Mena

03/01/2023, 2:13 PM

the problem here is that usually to call

validate

you don’t have a working value, you want to construct it when validation is successful

this may work with a prism, but would need a bit more work

dave08

03/01/2023, 2:15 PM

you don’t have a working value

I'm not sure I understand...? I fixed up my example above, we already HAVE an instance of foo... we're just returning it if it validates.

Just like you run

copy { }

on an instance.

this may work with a prism

I really don't understand what a prism IS (or any other of these constructs except for setter and getter...)

And there's no tutorials out there that explain it apart from those docs being worked on...

I was looking at the Copy implementation, and was thinking maybe something like this might be easier/more flexible? Is this possible @Alejandro Serrano Mena?

val foo = Foo(...)

val result: Either<ValidationError, Foo> = foo.validate {
   Foo.baz ensureThat { it == 20 }
   Foo.bar.bara.barb ensureThat { it.startsWith("something") }
 }

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