Default values

[gyzerok]

What do you think about having an ability to define default value. So if value is null or undefined it is got swapped with the value provided.

t.fromValidation(null, t.withDefault(t.string, 'hello world')) // 'hello world'

[gcanti]

I think that is already possible

function withDefault<T extends t.Any>(type: T, defaultValue: t.TypeOf<T>): t.Type<t.TypeOf<T>> {
  return new t.Type(
    type.name,
    (v, c) => type.validate(v != null ? v : defaultValue, c)
  )
}

[gyzerok]

Yeah, that make sense. I would try it as you described in my code and see if it's helpful. If it is, I guess we can discuss making it part of API.

[gunzip]

while this worked for properties in partial types as well until 0.9.1, this does not validate / populate default values anymore in t.partial(s) because of some changes in 0.9.2. this was a breaking change for us :)

ref.

https://github.com/teamdigitale/digital-citizenship-functions/blob/tech-debt/lib/utils/default.ts
https://github.com/teamdigitale/digital-citizenship-functions/blob/tech-debt/lib/utils/__tests__/default.test.ts

[gcanti]

@gunzip links are broken, could you please provide a test case?

[gcanti]

I think I got a repro

export function withDefault<T extends t.Any>(type: T, defaultValue: t.TypeOf<T>): t.Type<t.InputOf<T>, t.TypeOf<T>> {
  return new t.Type(
    `withDefault(${type.name}, ${JSON.stringify(defaultValue)})`,
    type.is,
    (v, c) => type.validate(v != null ? v : defaultValue, c),
    type.serialize
  )
}

const T1 = t.partial({
  name: withDefault(t.string, 'foo')
})

console.log(t.validate({}, T1).fold(() => 'error', a => JSON.stringify(a)))
// => `{}`

Related commit 37c74a5

My opinion is that it's better to give the passed type a chance to perform a deserialization and, in case of failure, fallback to undefinedType. I'll revert that change.

[gunzip]

sorry, here are the correct links:

https://github.com/teamdigitale/digital-citizenship-functions/blob/master/lib/utils/default.ts

https://github.com/teamdigitale/digital-citizenship-functions/blob/master/lib/utils/__tests__/default.test.ts

[safareli]

This is the version for decoders that I use:

export function withDefault<T extends D.Decoder<unknown, unknown>>(
  decoder: T,
  defaultValue: D.TypeOf<T>
): D.Decoder<D.InputOf<T>, D.TypeOf<T>> {
  return D.union(
    decoder,
    pipe(
      undefinedDecoder,
      D.map(() => defaultValue)
    )
  );
}

export const undefinedDecoder = {
  decode: (val: unknown) => {
    return val === undefined
      ? D.success(undefined)
      : D.failure(val, "undefined");
  },
};