[LLVMbugs] [Bug 22354] New: generic lambda capture fails with undefined reference to custom copy ctor

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Jan 27 09:47:11 PST 2015


            Bug ID: 22354
           Summary: generic lambda capture fails with undefined reference
                    to custom copy ctor
           Product: clang
           Version: 3.5
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++14
          Assignee: unassignedclangbugs at nondot.org
          Reporter: attugithub at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

When passing an object with custom copy ctor to generaic lambda capture
code compiles but fails to link with undefined reference to copy ctor.

template <typename> struct custom_copy_ctor {
  custom_copy_ctor() = default;
  custom_copy_ctor(custom_copy_ctor const &) {}
  // custom_copy_ctor(custom_copy_ctor const&) = default; // works fine

int main() {
  custom_copy_ctor<void> cc;
  [cc](auto) {}(1);
  //[cc](int){}(1); // works fine
  return 0;

$ clang++-3.5 -std=c++14 main.cc 
  /tmp/main-d01cbf.o: In function `main':
  main.cc:(.text+0x21): undefined reference to
`custom_copy_ctor<void>::custom_copy_ctor(custom_copy_ctor<void> const&)'
  clang: error: linker command failed with exit code 1 (use -v to see

$ clang++-3.5 --version
  Debian clang version 3.5.0-9 (tags/RELEASE_350/final) (based on LLVM 3.5.0)
  Target: x86_64-pc-linux-gnu
  Thread model: posix

Declaring copy ctor =default prevents the issue.
Problem does not occure also when "non-generic" lambda is used
(without template function call operator)

example with online compiler

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