Cannot insert into set. Please help.

I'm having trouble. I cannot call the insert() member function of set.

The error is caused by line 218 of this Gist: https://gist.github.com/sjhalayka/3fe4333ed0588cca075a29b3b831ab3d

I don't think I'm doing anything special. I've tried all kinds of things, but nothing helps.

Thanks for any time you may have.