# tagged enums

tagged enums let one pointer refer to a value with one of several payload shapes. a member with fields is declared using a block of field declarations; a member without fields has no block:

```zc
enum shape { circle { int r; }, rect { int w; int h; }, dot };
int area(shape* s) {
    switch (s) {
    case circle(r): return r * r * 3;
    case rect(w, h): return w * h;
    case dot: return 0;
    }
    return -1;
}
```

each constructor allocates an owned enum object and returns a pointer. word zero stores the tag; payload fields follow it. the object is sized for the largest member, and unused payload words are zeroed. a `case member(names)` arm tests the tag and binds that member's fields as locals scoped to the arm. a member omitted from a switch without `default` produces a warning, in typed and untyped code.

see [the tagged enum example](../../examples/learn/16-tagged-enums.zc). the syntax and behavior described here are implemented by the parser, typechecker, code generator and language server.