Re: Reserve_Capacity for Unbounded_String?

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Maciej Sobczak <see.my.homepage@gmail.com> writes:

> Why there is no Reserve_Capacity for Unbounded_String?

Probably for historical reasons.

> Sounds like a natural idea to me.

Yes.

> How to emulate it?
>
> The following seems to work fine:
>
> declare
>    S : Unbounded_String;
>    My_Capacity : constant := 1000;
> begin
>    S := To_Unbounded_String (My_Capacity);

I would write

  To_Unbounded_String (Length => My_Capacity);

to make it clear which To_Unbounded_String you're calling.

>    Delete (Source => S, From => 1, Through => My_Capacity);
>    -- ...
> end;
>
> "Seems to work fine" means that after the above two operations the
> string is logically empty, but the subsequent appends run faster
> (which is actually the original motivation).

How much faster (I'm curious)?

> Is this a reasonable approach if performance is of concern?

I think so.

- Bob