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EPWN3D • yesterday at 6:49 PM • 2 replies • view on HN

I would love for `union`s to be federated, that is, a type could declare itself as thought it was part of a union with another type, without having to pre-declare all possible types in one place.

Replies

Joker_vD • today at 9:04 AM

Can't you just declare anonymous unions whenever? E.g.

    struct foo { ... };
    
    struct bar { ... };

    struct bar check_this_out(struct foo foo) {
        return ((union { struct foo foo; struct bar bar; }){ .foo = foo}).bar;
    }

    struct bar *also_this(struct foo *foo) {
        union { struct foo foo; struct bar bar; } *tmp = (void*)foo;
        return &tmp->bar;
    }
o11c • yesterday at 7:02 PM

For layout-compatible types, you can often just include a `_base` member in each child. Maybe twice (once named and once unnamed) to avoid excess typing - I don't understand the common-initial-subsequence rule but people do this enough that compilers have to allow it.

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