C++ is weird. | Together C & C++ | Page 1

cobalt grove Dec 17, 2022, 1:12 PM

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Why is the following legal:

struct List{
    std::variant<int, std::vector<List>> data;
};

but this isn't legal?

using Integer = int;
using List = std::variant<Integer, std::vector<List>>;

radiant sedgeBOT Dec 17, 2022, 1:12 PM

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hollow glade Dec 17, 2022, 1:54 PM

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cobalt grove Why is the following legal: ```cpp struct List{ std::variant<int, std::vecto...

for the first one, same reason this is legal

struct Node {
  Node* next;
};

incomplete types can still be named in certain contexts where the type isn't required to be complete

for the second, an alias isn't a type and cannot be forward declared, the alias cannot behave like an incomplete type

cobalt grove Dec 17, 2022, 2:18 PM

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hollow glade for the first one, same reason this is legal ```cpp struct Node { Node* next; ...

I see, so I can't use an alias as a type in the alias definition? (not even sure if definition is the correct word here)

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Kinda of like the same way I can't do something like:

struct A {
  A foo;
};

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?

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I mean one is using a undeclared identifier and the other is using a incomplete type, but I think they are similar scenarios

fickle wraith Dec 17, 2022, 2:58 PM

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Maybe if using Integer; was made legal it would work.

radiant sedgeBOT Dec 18, 2022, 3:46 AM

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#C++ is weird.