alt Hacker NewsThis is addressed in the footnotes. casting is not the core of the type safety. Read the whole article.
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Ah, that’s what I get for not reading the footnotes. However, the alternative solution presented evaluates the item argument twice, which is problematic as well (but could probably be worked around by passing `(list)->payload` on instead). Secondly, the assignment for type-checking doesn’t work for read-only operations on a const List, or does it? And doesn’t the assignment overwrite the head? Lastly, the do-while construction means you can’t use it for operations that return a value (without compiler extensions).
I also don’t agree it’s “squeamish” to be wary of aliasing analysis going wrong. It’s not a clean abstraction and can hide subtle bugs down the road.
Sure, but your alternative code incorrectly assigns to (list)->payload. You have many other options. Without typeof, you can if(0) the assignment, or check type compatibility with a ternary operator like 1 ? (item) : (list)->payload and pass that to _list_prepend, etc. With typeof, you can store item in a temporary variable with the same type as (list)->payload, or build a compound literal (typeof(*(list))){.payload=(item)}, etc.
Working with function pointers is always finicky. I once had MSVC fold together
into a single function, so at runtime, (void(*)())f0 and (void(*)())f1 would compare equal. AFAIK, you are not guaranteed by the standard that functions of different signatures would, when their addresses are taken, result in different pointers, so it's not technically a bug... but it's quite surprising, and ruins certain tricks.