[lalaithion]

Good point. For example,

    type NotAProduct = Bool | Bool

only has 2 values, not 4. For a real product type, we need

    type Product = {tag: "Left", value: Bool} | {tag: "Right", value: Bool}

which has the requisite 4 values.

[feoren]

This is also called a "discriminated union", with "tag" being the discriminator here.

[nyanpasu64]

So to replicate a Rust enum, C tagged union, or C++ std::variant containing one byte for the type and the rest of the object inline, JavaScript needs a boxed object wrapping a string and the actual object contained inside? And the engine can't optimize away the boxed object into an inline value type because it could have multiple aliasing references in multiple locations? Boxing-based languages make me sad.