(declared implicitly) cannot be referenced -- it is a deleted function

With following code I'm facing an issue: ABC.h

namespace abcd
{

    class ABC
        {
        public:
              ABC() = delete;
              ABC(const std::string& filename);
              virtual ~ABC();
              ABC(const ABC&) = delete;
              ABC(ABC&&) = default;
         }
}

XYZ.h

using namespace abcd;
Class XYZ
{
 public:
        void func();
 private:          
        ABC obj;
        ABC maskfilename(std::string filename);
}

XYZ.cpp

XYZ::func()
{
        obj = maskfilename("abcd.txt"); //Error
}

abcd::ABC XYZ::masked(string filename)
{
    abcd::ABC ret;

    blah blah...

    return ret;
}

Error: "abcd::ABC::operator=(const abcd::ABC &)" (declared implicitly) cannot be referenced -- it is a deleted function

I understand it is move constructor only class (ABC). What is the right way to use this? I want to retain return value from maskfilename in the XYZ class, So it can be used in other functions of XYZ class. How can I resolve this error?