Re: Two approaches of iterators for the key-value pairs

[ytomino <aghia05@gmail.com>]

> > > Both choices could be made to have the same interface for the user, with the only difference being whether "in" or "of" appears in the loop.
> > 
> > Yes.
> > (And, Hashed_Maps/Ordered_Maps already use "in". So I felt "in" is suitable.)
> 
> Not sure what you mean here. Hashed_Maps/Ordered_Maps also already uses "of", 
> you can use either today, so how is one more suitable than the other?
> I think the "of" form involves less clutter that that user has to write, so I would generally try to use that, unless you really need a Cursor somewhere in the loop.

Well, Hashed_Maps/Ordered_Maps don't have a pair type similar to Name_Value_Pair_Type.

  for E of The_Map_Object loop

This E is Element_Type. We can not get the key of it with "of".
In this case, the indexing function accepting Cursor is Element or Reference, and it returns Element_Type.
On the other hand, in AI:

  for Pair of Ada.Environment_Variables.All_Variables loop

This Pair is Name_Value_Pair_Type.
The indexing function accepting Cursor is Current_Variable, and it returns not String but Name_Value_Pair_Type.
I think this difference prevents us from writing a generic subprogram for common use.

Sorry that the explanation of mine was lacking.

By the way, the indexing function of std::map of C++ STL returns a pair.
I have been pointed out it by one C++ user.