[llvm-bugs] [Bug 51348] New: llvm::Optional doesn't work well with move-only types

via llvm-bugs llvm-bugs at lists.llvm.org
Wed Aug 4 14:18:21 PDT 2021


https://bugs.llvm.org/show_bug.cgi?id=51348

            Bug ID: 51348
           Summary: llvm::Optional doesn't work well with move-only types
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Support Libraries
          Assignee: unassignedbugs at nondot.org
          Reporter: lemo1234 at gmail.com
                CC: llvm-bugs at lists.llvm.org

`llvm::Optional<T>` doesn't work well when T is a move-only type.

Repro: https://godbolt.org/z/adPEfaaEa

#include <llvm/ADT/Optional.h>

#include <vector>
#include <optional>

int main() {
    using X = std::unique_ptr<int>;

    using Y = llvm::Optional<X>; // fails to compile
    //using Y = std::optional<X>; // compiles fine

    std::vector<Y> z;
    z.push_back(std::make_unique<int>(42));
}

The problem seems to be traced to the following?

std::_Construct(std::__addressof(*__cur), *__first);

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