Effect CommunityEC
Effect Community•14mo ago
Janosch

Handling branded types with optional and nullish values can indeed be a bit tricky, especially wh...

I have a question regarding branded types and Schema.optionalToOptional. I get data from extern and it can be in a wild shape sometimes.

- Strings can be null
- Strings can be missing
- Strings can be empty

The first two requirements are simple, they can be represented using Schema.NullishOr(Schema.String). So whether I expect a branded type or not I can do either Schema.NullishOr(Schema.String) or Schema.NullishOr(Schema.String.pipe(Schema.fromBrand(myBrand)). So far so good.
Now for the last part. Removing empty strings is recommended in the Docs by using Schema.requiredToOptional or Schema.optionalToOptional.

So if I want to treat null as missing, empty string as missing (and missing strings as missing), I came to this solution:

export const StringFromNullish = Schema.optionalToOptional(
  Schema.NullOr(Schema.String),
  Schema.NonEmptyString,
  {
    decode: (input) => {
      if (Option.isNone(input)) {
        return Option.none();
      }
      const value = input.value;
      if (value === null || value.trim() === '') {
        return Option.none();
      }
      return Option.some(value);
    },
    encode: identity,
  },
);


Naming might not be accurate, I am still working on this. But the gist is: Any null value is omitted, and then null or empty strings are also omitted. Only if there actually is a non empty string, we keep it. This is awesome!
But with this I loose the ability to brand my strings (or at least I do not know how, this is the part that I struggle with).

Do I really need to define this Schema for every of my brand schemas?

export const MyBrandTypeFromNullish = Schema.optionalToOptional(
  Schema.NullOr(Schema.String.pipe(Schema.fromBrand(MyBrand))),
  Schema.NonEmptyString,
...

export const MyOtherBrandTypeFromNullish = Schema.optionalToOptional(
  Schema.NullOr(Schema.String.pipe(Schema.fromBrand(MyOtherBrand))),
  Schema.NonEmptyString,
...


Any help is appreciated!
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