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

["Alexandre E. Kopilovitch" <aek@vib.usr.pu.ru>]

Robert I. Eachus wrote:

> Randy Brukardt wrote:
>
> ...
>
> No, actually it wouldn't. It would make a lot of existing code ambiguous.
> 
>   A : Unbounded_String;
>   B : Unbounded_String := A & "something";
> 
> Since the string literal could have either type String or Unbounded_String,
> and "&" can have operands of either type, the expression would become
> ambiguous.
>
> Ouch! I forgot about that case when explaining why the non-literal 
> conversions would be ambiguous.  Having worked on this though, you can 
> handle it as you say by a completely new package with different 
> overloadings of "&"--which won't happen.

Actually there is no need for completely new package with different overloadings of "&"
- just one little new pragma seems sufficient:

  pragma Non_Literal_Argument(subroutine-name, parameter-name);

stating (immediately following the function's spec) that actual argument for
this parameter cannot be a literal. That is, the whole spec for that "&" will be:

  function "&" (Left : in Unbounded_String; Right : in String)
     return Unbounded_String;
  pragma Non_Literal_Argument("&", Right);

and that unhappy ambiguity disappears forever.



Alexander Kopilovitch                      aek@vib.usr.pu.ru
Saint-Petersburg
Russia