Marc Mintel
5397309103
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41 lines
1.4 KiB
Plaintext
41 lines
1.4 KiB
Plaintext
/**
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Create an opaque type, which hides its internal details from the public, and can only be created by being used explicitly.
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The generic type parameter can be anything. It doesn't have to be an object.
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[Read more about opaque types.](https://codemix.com/opaque-types-in-javascript/)
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There have been several discussions about adding this feature to TypeScript via the `opaque type` operator, similar to how Flow does it. Unfortunately, nothing has (yet) moved forward:
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- [Microsoft/TypeScript#15408](https://github.com/Microsoft/TypeScript/issues/15408)
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- [Microsoft/TypeScript#15807](https://github.com/Microsoft/TypeScript/issues/15807)
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@example
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```
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import {Opaque} from 'type-fest';
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type AccountNumber = Opaque<number>;
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type AccountBalance = Opaque<number>;
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function createAccountNumber(): AccountNumber {
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return 2 as AccountNumber;
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}
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function getMoneyForAccount(accountNumber: AccountNumber): AccountBalance {
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return 4 as AccountBalance;
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}
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// This will compile successfully.
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getMoneyForAccount(createAccountNumber());
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// But this won't, because it has to be explicitly passed as an `AccountNumber` type.
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getMoneyForAccount(2);
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// You can use opaque values like they aren't opaque too.
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const accountNumber = createAccountNumber();
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// This will compile successfully.
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accountNumber + 2;
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```
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*/
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export type Opaque<Type> = Type & {readonly __opaque__: unique symbol};
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