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From: "REH" <spamjunk@stny.rr.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada to C++ translator
Date: 25 Jan 2006 15:19:14 -0800
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Date: 2006-01-25T15:19:14-08:00
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Gautier Write-only wrote:
> Also, one point where a translation could look more like a
> compilation is Ada's possibility of nesting subprograms or
> packages into other subprograms or packages.
> E.g. what is the C++ equivalent of the following (silly,
> but correct) code ?
>
> with Ada.Text_IO;
>
> procedure Nest_Test is
>
>   procedure P1(s1: String) is
>
>     procedure P2(s2: String) is
>     begin
>       if s2'Length > 0 then
>         declare
>           generic
>             content: String;
>           package K1 is
>             procedure Spit;
>           end K1;
>           package body K1 is
>             procedure Spit is
>             begin
>               Ada.Text_IO.Put(content(content'First));
>               P1(content(content'First+1..content'Last));
>             end Spit;
>           end K1;
>           package my_K1 is new K1( content=> s2 );
>         begin
>           my_K1.Spit;
>         end;
>       end if;
>     end P2;
>
>   begin
>     P2(s1);
>   end P1;
>
> begin
>   P1("A very silly way to display a string!");
> end Nest_Test;


These are great features of Ada, ones that I wish C++ had.  The closed
I could come to the above is:

#include <string>
#include <iostream>

void Nest_Test() {

    struct P1 {
        P1(const std::string& s1)
        {
            struct P2 {
                P2(const std::string& s2)
                {
                    struct Spit {
                        Spit(const std::string& s2)
                        {
                            std::cout << s2[0];
                            P1(s2.substr(1));
                        }
                    };

                    if (!s2.empty())
                    {
                        Spit s(s2);
                    }
                }
            };

            P2 p(s1);
        }
    };

    P1 p("A very silly way to display a string!");
}

But it definitely is not as nice.  And there is no way to define local
templates, nor instantiate them with dynamic data.