Function extendTo

packages/effect/src/Schema.ts:3728–3763

(
  /** The new fields to add */
  fields: Fields,
  /** A function per field to derive its value from the original input */
  derive: { readonly [K in keyof Fields]: (s: S["Type"]) => Option_.Option<Fields[K]["Type"]> }
)

 * @since 4.0.0
 */
export function extendTo<S extends Struct<Struct.Fields>, const Fields extends Struct.Fields>(
  /** The new fields to add */
  fields: Fields,
  /** A function per field to derive its value from the original input */
  derive: { readonly [K in keyof Fields]: (s: S["Type"]) => Option_.Option<Fields[K]["Type"]> }
) {
  return (
    self: S
  ): decodeTo<Struct<Simplify<{ [K in keyof S["fields"]]: toType<S["fields"][K]> } & Fields>>, S> => {
    const f = Record_.map(self.fields, toType)
    const to = Struct({ ...f, ...fields })
    return self.pipe(decodeTo(
      to,
      SchemaTransformation.transform({
        decode: (input) => {
          const out: any = { ...input }
          for (const k in fields) {
            const f = derive[k]
            const o = f(input)
            if (Option_.isSome(o)) {
              InternalRecord.assignProperty(out, k, o.value)
            }
          }
          return out
        },
        encode: (input) => {
          const out = { ...input }
          for (const k in fields) {
            delete out[k]
          }
          return out
        }
      })
    )) as any
  }
}

/**
 * Namespace for `Record` type utilities.