Value Objects – DDD with TypeScript

Re:Value Objects – DDD with TypeScript by spankalee on Monday April 08, 2019 @12:26AM (#19602077)

You can do much better than just a type alias in TypeScript, and get specializations of primitives that type check and compile away.

    type Path = string & { _brand: never };
    
    const Path = (s: string) => validatePath(s) as Path;
    
    const p1: Path = Path('/foo/bar.js');
    const p2: Path = '/foo/bar.js';

Here, p2 has an error because a string is not assignable to a Path.

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Re:Value Objects – DDD with TypeScript by skybrian on Monday April 08, 2019 @02:33AM (#19602662)

That's a neat trick! I went searching for articles about it and came up empty, though I did find other interesting uses of the "never" type.

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