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

["Randy Brukardt" <randy@rrsoftware.com>]

"Robert I. Eachus" <rieachus@comcast.net> wrote in message
news:3F88E067.30209@comcast.net...
> Now if you want to recommend that in Ada 200X, package
> Ada.Strings.Unbounded include:
>
>     function "+" (Source : in String) return Unbounded_String
>        renames To_Unbounded_String;
>     function "+" (Source : in Unbounded_String) return String
>        renames To_String;
>
> I will certainly support that.  I don't really know why they were left
> out of Ada.Strings.Unbounded while

They were briefly in AI-301's improvements to Ada.Strings, but enough people
think that they're ugly that they were taken out.

Earlier, Robert said:

> And as I said, I think adding implicit conversion of string literals to
> and from Unbounded_String would work.

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.

It's virtually impossible to "improve" the current Ada.Strings.Unbounded.
We'd have to create a whole new package for that, and that would be a tough
sell for the standard. My preference would be a package in which String
occurs only in the To_xxx routines, along with a way to use string literals
directly as Unbounded_Strings. (Non-literal conversions from String should
be explicit.) That would be a much more consistent abstraction than
Ada.Strings.Unbounded. But we're pretty much stuck with
Ada.Strings.Unbounded as it is.

                 Randy.