Prototype: Discriminated Union

example/prototypes/discriminated-union.ts

@@ -0,0 +1,96 @@
+
+/*--------------------------------------------------------------------------
+
+@sinclair/typebox/prototypes
+
+The MIT License (MIT)
+
+Copyright (c) 2017-2024 Haydn Paterson (sinclair) <[email protected]>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+
+---------------------------------------------------------------------------*/
+
+import { Static, Kind, TSchema, TObject, SchemaOptions, CreateType, TLiteral, TypeRegistry, ValueGuard, KindGuard, TUnion } from '@sinclair/typebox'
+import { GetErrorFunction, SetErrorFunction } from 'src/errors/function'
+import { Value } from '@sinclair/typebox/value'
+
+// ------------------------------------------------------------------
+// DiscriminatedUnionError
+// ------------------------------------------------------------------
+const errorFunction = GetErrorFunction()
+
+// prettier-ignore
+SetErrorFunction((parameter) => {
+  if (parameter.schema[Kind] !== 'DiscriminatedUnion') {
+    return errorFunction(parameter)
+  }
+  const union = parameter.schema as TDiscriminatedUnion
+  // Try generate error when value matches known discriminator literal
+  if (ValueGuard.IsObject(parameter.value) && union.discriminator in parameter.value) {
+    const variant = parameter.schema.anyOf.find((variant: TSchema) => union.discriminator in variant.properties
+      && (variant.properties[union.discriminator] as TLiteral).const ===
+      (parameter.value as Record<PropertyKey, unknown>)[union.discriminator])
+    if (KindGuard.IsSchema(variant)) {
+      const literal = variant.properties[union.discriminator]
+      return `Invalid value for DiscriminatedUnion variant '${literal.const}'`
+    }
+  }
+  // Return generic error containing possible discriminator types.
+  const options = union.anyOf.map(object => object.properties[union.discriminator].const) as string[]
+  return `Expected value of ${options.map(option => `'${option}'`).join(', ')} for DiscriminatedUnion`
+})
+
+// ------------------------------------------------------------------
+// TDiscriminatedUnionObject
+//
+// Constructs a base TObject type requiring 1 discriminator property
+// ------------------------------------------------------------------
+// prettier-ignore
+type TDiscriminatedUnionProperties<Discriminator extends string> = {
+  [_ in Discriminator]: TLiteral
+}
+// prettier-ignore
+type TDiscriminatedUnionObject<Discriminator extends string> = TObject<TDiscriminatedUnionProperties<Discriminator>>
+
+// ------------------------------------------------------------------
+// DiscriminatedUnion
+// ------------------------------------------------------------------
+// prettier-ignore
+TypeRegistry.Set('DiscriminatedUnion', (schema: TDiscriminatedUnion, value) => {
+  return schema.anyOf.some(variant => Value.Check(variant, [], value))
+})
+// prettier-ignore
+export interface TDiscriminatedUnion<Discriminator extends string = string, Types extends TObject[] = TObject[]> extends TSchema {
+  [Kind]: 'DiscriminatedUnion'
+  static: Static<TUnion<Types>>
+  discriminator: Discriminator
+  anyOf: Types
+}
+
+/** Creates a DiscriminatedUnion. */
+// prettier-ignore
+export function DiscriminatedUnion<Discriminator extends string, Types extends TDiscriminatedUnionObject<Discriminator>[]>(
+  discriminator: Discriminator, types: [...Types], options?: SchemaOptions
+): TDiscriminatedUnion<Discriminator, Types> {
+  return CreateType({ [Kind]: 'DiscriminatedUnion', anyOf: types, discriminator }, options) as never
+}
+
+
+

example/prototypes/index.ts

@@ -26,6 +26,7 @@ THE SOFTWARE.
 
 ---------------------------------------------------------------------------*/
 
+export * from './discriminated-union'
 export * from './from-schema'
 export * from './partial-deep'
 export * from './union-enum'