Ranges: is it ok if front is a data member?

[Joseph Rushton Wakeling]

On 13/12/13 16:52, Marco Leise wrote:
> Most non-trivial ranges do the actual work in `popFront()' and
> return a cached value from `front'. It has been argued as a
> design quirk, that this in general leads to:
>
> struct Range
> {
>    bool popFrontHasBeenCalledOnce = false;
>    T current;
>
>    @property T front()
>    {
>      if (!popFrontHasBeenCalledOnce)
>      {
>        popFront();  // initializes `current'
>      }
>      return current;
>    }
>
>    […]
> }

For example in much of std.random.  With classes you can get round it by 
defining a default constructor, but with structs it can create some tricky 
situations.

I have wondered about the feasibility of a method called something like .first() 
which would basically be called the very first time one calls _any_ method of 
the struct/class in question, and would perform the appropriate initialization.