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[BUG] Parameter direction for template parameter is ignored #425
Description
Title: Parameter direction for template parameter is ignored.
Minimal reproducer (https://cpp2.godbolt.org/z/M1jxGdeqe):
a: <in T> type = { }
b: <in V: _> type = { }
main: () = { }
Commands:
cppfront -clean-cpp1 main.cpp2
clang++17 -std=c++2b -stdlib=libc++ -lc++abi -I . main.cppExpected result:
For the : type case, a diagnostic.
For the : _ case, adherence to the specified parameter direction.
template<typename T> class a; // A Cpp2 diagnostic here.
template<const auto& V> class b;Actual result and error:
template<typename T> class a;
template<auto V> class b;Program returned: 0
Cpp2 lowered to Cpp1.
#include "cpp2util.h"
template<typename T> class a;
template<auto V> class b;
template<typename T> class a {
public: a() = default;
public: a(a const&) = delete; /* No 'that' constructor, suppress copy */
public: auto operator=(a const&) -> void = delete;
};
template<auto V> class b {
public: b() = default;
public: b(b const&) = delete; /* No 'that' constructor, suppress copy */
public: auto operator=(b const&) -> void = delete;
};
auto main() -> int;
auto main() -> int{}
Activity
realgdman commentedon May 13, 2023
Possibly related: I'm using library (flecs) with API like
And haven't found way to specify that
constin template call to system()Which, I believe, cannot be deduced from parameters of lambda
https://cpp2.godbolt.org/z/sjMWTq3b7
JohelEGP commentedon May 13, 2023
Seems like a bug: https://cpp2.godbolt.org/z/Tx8e9KfKc.
I suggest you open a new issue, since this one is about template parameters, not template arguments.
realgdman commentedon May 13, 2023
Ok, I do later, what I mean by related is, should I be able to put
inin <> in that case.JohelEGP commentedon May 13, 2023
I don't think that can work.
In a subexpression, a parameter direction operates on an expression, not a type.
cppfrontdoesn't have enough semantic information forf<in int>()to work.hsutter commentedon Aug 13, 2023
Yes, this is by design -- I don't know what it would mean.
I should probably emit a diagnostic for it though. Thanks!
BREAKING CHANGE: Change contracts syntax to align with P2661R1
Add diagnostic to disallow a parameter-direction on a template parame…
Add diagnostic to disallow a parameter-direction on a template parame…