Thread: add subscription operator if the value provide it.

[mjklaim@…]

I would like to be able to do

    typedef boost::synchronized_value< boost::container::flat_map<int, int> > ValueIndex;
    
    ValueIndex index;
    index[0] = 1;

and would expect that last line to be equivalent to

    auto locked_index = index.synchronize();
    (*locked_index)[0] = 1;

I'm not totally sure it's possible to do but it would help.