[AnIdiotOnTheNet]

> - `union` is an unchecked sum type, similar to a c union without a tag field.

My understanding was that Zig unions are tagged, but if you don't explicitly specify the tag type the compiler will choose for you. Indeed, the first example in the documentation suggests normal unions are tagged:

  // A union has only 1 active field at a time.
  const Payload = union {
      Int: i64,
      Float: f64,
      Bool: bool,
  };
  test "simple union" {
      var payload = Payload {.Int = 1234};
      // payload.Float = 12.34; // ERROR! field not active
      assert(payload.Int == 1234);
      // You can activate another field by assigning the entire union.
      payload = Payload {.Float = 12.34};
      assert(payload.Float == 12.34);
  }

Or do straight unions only get a hidden tag for debug/safe builds? My memory is a little fuzzy.