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webshrine / stdtyp/src / Brand

Type Alias: Brand<T, U> ​

Brand<T, U>: T & object

Brand

Type declaration ​

__brand ​

__brand: U

Type Parameters ​

• T

• U

Desc ​

Define nominal type of U based on type of T. Similar to Opaque types in Flow.

Example ​

ts
type USD = Brand<number, "USD">
  type EUR = Brand<number, "EUR">

  const tax = 5 as USD;
  const usd = 10 as USD;
  const eur = 10 as EUR;

  function gross(net: USD): USD {
    return (net + tax) as USD;
  }

  // Expect: No compile error
  gross(usd);
  // Expect: Compile error (Type '"EUR"' is not assignable to type '"USD"'.)
  gross(eur);

Defined in ​

node_modules/.pnpm/utility-types@3.11.0/node_modules/utility-types/dist/mapped-types.d.ts:432