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by clownstrikelol 60 days ago
That’s barely scratching the surface.

In TypeScript the following is also valid:

class Something{

    value: Number
}

class SomethingElse{

    value: Number

    foo: String

    bar: SomeOtherThing[]
}

function AddSomething(v: Something)

{

    v.value += 1;
}

var ex = new SomethingElse{

    value: 3,

    foo: “TypeScript is fake types”,

    bar: []
};

AddSomething(ex);

Why does it work? Because in TypeScript as long as you have a “shape” that fits, it’s the “same type.”

Complete and utter insanity to me, to pretend there’s any real type checking, when types are entirely fake and made up.
1 comments
saghm 60 days ago
That's because it's structurally typed (as opposed to nominally typed). I don't happen to prefer it, but I don't think it's fair to conflate that with unsoundness like the example given above; it's totally possible to have a sound structural type system. TypeScript doesn't happen to be sound, but it's not because of that.
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teaearlgraycold 60 days ago
Structural typing is great. It's the verified version of duck typing.
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LelouBil 60 days ago
You can even get nominal typing with branded types if you need it. (Like for the newtype pattern)
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