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No. This is how sum types are implemented. And from a runtime perspective it’s going to be a struct with perhaps more padding. You’ll need more details about y

No. This is how sum types are implemented. And from a runtime perspective it’s going to be a struct with perhaps more padding. You’ll need more details about your specific threat model to explain why that’s bad.

mistrial9 1y ago
a quick search says that std::variant is the modern replacement to implement your niche feature "sum types"
- grandempire 1y ago
  That’s for C++. And how is std::variant implemented?
  - LowLevelMahn 1y ago
    not using a union: https://ojdip.net/2013/10/implementing-a-variant-type-in-cpp/ https://ojdip.net/2013/10/implementing-a-variant-type-in-cpp... because the union can't be extended with variadic template types
    - grandempire 1y ago
      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.
    - LegionMammal978 1y ago
      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/include/std/variant;hb=refs/tags/releases/gcc-15.1.0#l386 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/libcxx/include/variant#L671 https://github.com/llvm/llvm-project/blob/llvmorg-20.1.3/lib...
- jlouis 1y ago
  Not a niche feature. Fundamental for any decent language with a type system.
  - mistrial9 1y ago
    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 1y ago
      std::variant does not exist in C99.
- soraminazuki 1y ago
  Whoa, that's a core building block of programming and computer science that you're dismissing as "niche" without explanation.
  - mistrial9 1y ago
    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 1y ago
      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.

mistrial9 1y ago

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

grandempire 1y ago
That’s for C++. And how is std::variant implemented?
- LowLevelMahn 1y ago
  not using a union: https://ojdip.net/2013/10/implementing-a-variant-type-in-cpp/ https://ojdip.net/2013/10/implementing-a-variant-type-in-cpp... because the union can't be extended with variadic template types
  - grandempire 1y ago
    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.
  - LegionMammal978 1y ago
    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/include/std/variant;hb=refs/tags/releases/gcc-15.1.0#l386 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/libcxx/include/variant#L671 https://github.com/llvm/llvm-project/blob/llvmorg-20.1.3/lib...
jlouis 1y ago
Not a niche feature. Fundamental for any decent language with a type system.
- mistrial9 1y ago
  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 1y ago
    std::variant does not exist in C99.
soraminazuki 1y ago
Whoa, that's a core building block of programming and computer science that you're dismissing as "niche" without explanation.
- mistrial9 1y ago
  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 1y ago
    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.