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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Strange compile-time error  with
 Ada.Containers.Indefinite_Hashed_Maps
Date: Mon, 19 May 2014 14:49:45 +0100
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Date: 2014-05-19T14:49:45+01:00
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mockturtle <framefritti@gmail.com> writes:

> I define the "identifier name" type in a package that is with-ed by
> the package that defines the symbol table.  The symbol table is just a
> Indefinite_Hash_Map (indefinite since the descriptor is indefinite).
> When I try to compile the body of the symbol table package I get in
> the .ads the error
>
>     instantiation error at a-cihama.adb:1043
>     invalid constraint: type has no discriminant

All of GNAT GPL 2013, FSF GCC 4.8.1 and FSF GCC 4.9.0 are happy with
your code.

a-cihama.adb (Ada.Containers.Indefinite_Hashed_Maps) line 1043 is in
Read_Node:

   function Read_Node
     (Stream : not null access Root_Stream_Type'Class) return Node_Access
   is
      Node : Node_Access := new Node_Type;

   begin
      begin
         Node.Key := new Key_Type'(Key_Type'Input (Stream)); <<<<<<

and I don't see why GNAT thinks there (should be?) a discriminant there.

Is there a reason why you don't make Name_Type just String? You're
forced to use indefinite hashed maps, so the stored Key is assumed to be
indefinite and will be allocated. (I tried this and the compiler was
happy).