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I have some extremely repetative code in TypeScript where I need to do essentially this dozens and dozens of times:

const IdPIdChangedDecoder = D.struct({
  newIdpId: UuidDecoder,
})
export type IdPIdChangedPayload = D.TypeOf<typeof IdPIdChangedDecoder>;
export const IdPIdChanged: EventMeta<Customer, IdPIdChangedPayload> = {
  name: EventNames.IdPIdChanged,
  decoder: IdPIdChangedDecoder,
  fn: (customer, p) => {
    return { ...customer, idpId: p.payload.newIdpId, lastUpdated: p.timestamp }
  },
}
export type IdPIdChanged = KnownEvent<EventNames.IdPIdChanged, EmailAddressChangedPayload>

As is evident the IdpIdChanged is repeated no less than 9 times in a single block.

Coming from Rust, I'd probably reach for a Macro in this scenario, because given a name, and a decoder, I could simply metaprogram that out.

In all my research however it seems like TypeScript compilers don't support anything like this in general?

Is there any general option to reduce the boilerplate? Bonus points if I can also eliminate the EventNames.IdpIdChanged enum (enum Eg { IdpIdChanged = "idp_id_changed" , }), and also add all the KnownEvent variants to a union type.

This is all boilerplate for an event driven system I am working on, and the various flavors of events, decoders, types, constants and such are all used in either the read, or write- side of the system, someplace or other.

I would have some limited flexibility in changing these types for a different paradigm, but not a great deal.

Lee Hambley
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  • Indeed TypeScript does not have built-in code generation feature. But you may still be able to scaffold your boilerplate with proper use of function or class and template literal types. Your code sample contains plenty undefined types, which is understandable if we are talking about code generation, but is a show stopper if we want to handle it through e.g. a function which can understand these types. If I try guessing them, I get [this](https://tsplay.dev/wOxlEN); if it is too far away from your actual types, can you fix them? – ghybs Dec 14 '22 at 02:02

0 Answers0