I have a question about the generated Optional opt...

# arrow

[Quantum64]

I have a question about the generated Optional optics for nullable fields. The laws for affine traversals state that "If you get nothing when extracting a value, then whatever you put in, the operation is no-op" (http://oleg.fi/gists/posts/2017-04-18-glassery.html#laws:affine-traversal). The generated code that I see for a nullable field is setting the value without checking if a value is present. Here's an example:

inline val TestOptics.Companion.nullable: arrow.optics.Optional<TestOptics, Int> inline get()= arrow.optics.Optional(
  getOrModify = { testOptics: TestOptics -> testOptics.`nullable`?.right() ?: testOptics.left() },
  set = { testOptics: TestOptics, value: Int -> testOptics.copy(`nullable` = value) }
)

Is the arrow Optional optic not equivalent to an affine traversal? If not, what is it equivalent to?

[Nathan Bedell]

I believe it is the same as an AffineTraversal.

[Quantum64]

If it is the same, then the generated code is incorrect. Calling set on an option where the focus is null should be a no-op

[simon.vergauwen]

cc\\ @Alejandro Serrano Mena

[simon.vergauwen]

For an Optional I think this is indeed correct. That sounds like the behavior of a Lens for a nullable field.