[llvm-bugs] [Bug 43944] New: Clang (front end) errors on variadic template operator=

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43944

            Bug ID: 43944
           Summary: Clang (front end) errors on variadic template
                    operator=
           Product: new-bugs
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: davidfink314 at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

Clang determines a variadic template operator= as taking 0 arguments (which it
then errors on, since it requires 1), no matter what arguments are actually
passed.


See godbolt, or the same code below:
https://godbolt.org/z/cqqnCb


<source>:21:20: error: overloaded 'operator=' must be a binary operator (has 1
parameter)
    decltype(auto) operator=(Args&&... args) {
                   ^
<source>:40:7: note: in instantiation of function template specialization
'mynamespace::vector<C, std::allocator<C> >::operator=<>' requested here
    c.operator=({getc()});





#include <vector>

namespace mynamespace {

template <class T, class Alloc = std::allocator<T>>
class vector : public std::vector<T, Alloc> {
  private:
    using Base = std::vector<T, Alloc>;

  public:
    template <class... Args>
    vector(Args&&... args)
        : Base(std::forward<Args>(args)...) {
    }

    vector(std::initializer_list<T> il)
        : Base(il) {
    }

    template<class... Args>
    decltype(auto) operator=(Args&&... args) {
        Base::operator=(std::forward<Args>(args)...);
        return *this;
    }
};

} /* namespace mynamespace */

struct C {
    int x;
};

C getc();

int main() {
    mynamespace::vector<C> c;
    // works
    c.operator=(mynamespace::vector<C>{getc()});
    //  doesn't work (= template errors on 0 params)
    c.operator=({getc()});
    // also doesn't work
    c = {getc()};
    // also doesn't work
    c = {getc(), getc()};
}

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