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C unions can provide compile-time type safety for generic data structures

danielchasehooper.com 9 min read Editor score 7/10

The technique uses unions to associate type information with generic C containers, allowing the compiler to reject a value of the wrong type. It is a practical pattern for engineers who need reusable data structures without giving up compile-time checks.

What

Union-based C generics associate type information with a data structure; the article illustrates the approach with a linked list.

How

Typed list declarations let `list_prepend` accept `Foo` values while rejecting an `int` for `List(Foo)` at compile time.

Why it matters

Compile-time checking can reduce type mismatches in generic C structures such as lists, maps, arrays, and trees.

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