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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Is this a bug in my code or the compiler?
Date: Fri, 12 Jun 2015 09:48:56 -0700
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Xref: news.eternal-september.org comp.lang.ada:26285
Date: 2015-06-12T09:48:56-07:00
List-Id: <comp.lang.ada>

On 06/12/2015 08:56 AM, David Botton wrote:
> Given:
> 
>    function Token_Start (Source : in out Awesome.Source.Source_Type'Class)
>                          return Character;
>    function Token_End (Source : in out Awesome.Source.Source_Type'Class)
>                        return String;
> 
> The following works:
> 
>    function Get_Token_Text (Source : in out Awesome.Source.Source_Type'Class)
>                             return String
>    is
>       N : Character := Token_Start (Source);
>    begin
>       return N & Token_End (Source);
>    end Get_Token_Text;
> 
> The following does not work:
> 
>    function Get_Token_Text (Source : in out Awesome.Source.Source_Type'Class)
>                             return String
>    is
>    begin
>       return Token_Start (Source) & Token_End (Source);
>    end Get_Token_Text;

Given that the Source parameters to both Token_Start and Token_End are mode "in
out", I presume that both functions modify Source and therefore, Token_Start
must be called before Token_End. Your 1st version ensures this order; your 2nd
does not. You are presuming an order of evaluation of the parameters to "&" that
is not guaranteed.

What happens if Token_End is called 1st?

-- 
Jeff Carter
"Unix and C are the ultimate computer viruses."
Richard Gabriel
99