D's appendto packaging

original text

struct AppendTo(T)
{
    
   private T[] *arr;
   this(return T[]* arr) {
     this.arr = arr; }
   void put(X)(X val) if (__traits(compiles, (*arr) ~= val)) {
    
      (*arr) ~= val;
   }
}

auto appendTo(T)(return ref T[] arr)
{
    
   return AppendTo!T(&arr);
}