Record keys are not transformed

[siikasmaa]

Hey there,

I have the assumption that Record type keys could be transformed e.g. the following way:

const A = Type.Transform(Type.String())
  .Decode(value => `key-${value}`)
  .Encode(value => value)

const B = Type.Number()

const C = Type.Record(A, B)

const result = Value.Parse(C, {
  '1': 1,
  '2': 2
})

The result is { '1': 1, '2': 2 } while my expectation is that it would be { 'key-1': 1, 'key-2': 2 }. The static type of result is never as there is no guard within Record which would check for Transform. Is this something that could be added? Interested to hear your thoughts before trying to add it myself.

[sinclairzx81]

@siikasmaa Hi, sorry for the delay

I have the assumption that Record type keys could be transformed e.g. the following way:

This is a general limitation with Transforms. As of the current version, Transform types cannot be used to transform Record keys, but do agree this feature would be ideal. The way to approach this is to wrap the Record in a exterior transform.

const T = Type.Transform(Type.Record(Type.String(), Type.Number()))
  .Decode(value => Object.keys(value).reduce((result, key) => {
      return { ...result, [`key-${key}`]: value[key] }
    }, {}) as Record<`key-${string}`, number>)
    .Encode(value => value)

const result = Value.Parse(T, { '1': 1, '2': 2 })

console.log({ result }) // { result: { 'key-1': 1, 'key-2': 2 } }

I am investigating ways to improve Key transformation in the next revision, but for now, the above is the way to approach things.

Will close up this issue for now, but happy to field any additional questions on this thread.
Cheers
S