a quick search says that std::variant is the modern replacement to implement your niche feature "sum types"

Not a niche feature. Fundamental for any decent language with a type system.

ok, but C99 and C++11 and others, all have ways to implement types. "Fundemental" as you say.. using UNION in C++ is not a good choice to implement types.. in old C99, you can use UNION that way but why? footguns all around.

	▲	saagarjha 8 months ago \| parent [-]
		std::variant does not exist in C99.

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soraminazuki 8 months ago | parent | prev | next [-]

Whoa, that's a core building block of programming and computer science that you're dismissing as "niche" without explanation.

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mistrial9 8 months ago | parent [-]

yes types are a core building block of programming and computer science, but not using UNION ? this casual dismissal of "criticisms of UNION" here seems superficial and un-wise to me.

	▲	soraminazuki 8 months ago \| parent [-]
		Sum types, not C unions. Different concepts. A sum type is a concept from type theory. Like unions, it expresses a type that can be either one of multiple types. But unlike unions, it retains information about which type it is. Properly implemented sum types are completely type safe. I can't be 100% sure what your particular "criticisms" of C unions precisely are, but assuming they all relate to type safety, they don't apply to sum types. Sum types are important because any real world project has to deal with data that's either A or B. There's nothing controversial here. In C, a union is a way to implement that. Yes, it's unsafe. But can you eliminate the use of unsafe features from C projects? No, if they deal with memory. Also, it's rich and quite frankly rude to brush off my comment as "casual dismissals," "superficial," and "unwise" when it's a direct response to this. > your niche feature "sum types" That's pure unprovoked smugness right there that contains no substance of what your criticisms actually are, let alone the reason.

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grandempire 8 months ago | parent | prev [-]

That’s for C++. And how is std::variant implemented?

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LowLevelMahn 8 months ago | parent [-]

not using a union: https://ojdip.net/2013/10/implementing-a-variant-type-in-cpp... because the union can't be extended with variadic template types

	▲	LegionMammal978 8 months ago \| parent \| next [-]
		Actually, it does use a union, in both libstdc++ [0] and libc++ [1]. (Underneath a lengthy stack of base classes, since it wouldn't be C++ if it weren't painful to match the specified semantics.) [0] https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=libstdc%2B%2B-v3... [1] https://github.com/llvm/llvm-project/blob/llvmorg-20.1.3/lib...
	▲	grandempire 8 months ago \| parent \| prev [-]
		So instead it has a buffer large enough to hold all the types? That’s what union does. Still waiting to hear the security concerns.