Re: U : Unbounded_String := "bla bla bla"; (was: Is the Writing...)

[Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>]

On Sun, 12 Oct 2003 05:03:09 GMT, "Robert I. Eachus"
<rieachus@comcast.net> wrote:

>String literals are a universal type that can be implicitly converted to 
>any string type.  As I said it would be possible to make this case legal 
>by making Unbounded_String (and presumably similar types) string types. 
>  But that would work against what you really want, since now, if you 
>also allow
>
>   Foo: String := "foo";
>   O_S : Unbounded_String := Foo; --implicit conversion
>   U_S : Unbounded_String := "literal"; -- Can't work now.
>                            ^ ambiguous could be:
>   function ""(L: string_literal) return Unbounded_String;
>or
>   function ""(L: string_literal) return String; followed by
>   function ""(L: String) return Unbounded_String;

and 

   function ""(L: string_literal) return String; followed by
   function ""(L: String) return Unbounded_String; followed by
   function ""(L: Unbounded_String) return String; followed by
   function ""(L: String) return Unbounded_String; followed by
   function ""(L: Unbounded_String) return String; followed by
   ...

Clearly domination rules a la C++ are required to disambiguate type
conversions. Moreover one will probably need some pragmas to
prioritize conversions. For instance, to ensure that for temp results
the compiler would prefer String over Unbounded_String.

It is not easy, though nobody claimed that it is! (:-))

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de