file i/o in a variety of languages

[Steven Schveighoffer]

On Fri, 27 Aug 2010 17:16:37 -0400, dsimcha <dsimcha at yahoo.com> wrote:

> == Quote from Steven Schveighoffer (schveiguy at yahoo.com)'s article
>> On Fri, 27 Aug 2010 16:41:58 -0400, Andrei Alexandrescu
>> <SeeWebsiteForEmail at erdani.org> wrote:
>> > On 8/27/10 13:28 PDT, Steven Schveighoffer wrote:
>> >> No, the code does this:
>> >>
>> >> f.writeln("hello");
>> >> f.writeln("world");
>> >>
>> >> The example is supposed to demonstrate how to re-open the file for
>> >> appending and write "world". Look at some of the other examples. Not
>> >> that it's a big deal, because I think it's just one more line.
>> >
>> > Oh, I understand now. Thanks.
>> BTW, Don pointed out the clarifcation that I missed.  It actually is
>> correct, my apologies.
>> >> I bring it up because people look at the C++ or C version and say  
>> "how
>> >> ugly, look how nice D looks," but the C++ version doesn't incur extra
>> >> allocations AFAIK. It's like commenting on how beautiful function  
>> qsort
>> >> looks. In reality, it's not as bad, because it's just that the
>> >> functionality isn't there yet. If it were, it would still look as
>> >> beautiful :) I just hate it when people compares an apple to orange  
>> and
>> >> comment on how the orange looks like a much better apple.
>> >
>> > I agree. In fairness, the same goes about comparing incorrect code  
>> with
>> > correct code. My understanding is that quite a few examples given in
>> > that thread are not correct, in spite of looking quite elaborate.
>> >
>> > FWIW it's not much aggravation to avoid unnecessary allocations:
>> >
>> > char[] line;
>> > f.readln(line);
>> > f.readln(line);
>> Hm.. this still allocates.  We can do better than the C++ example:
>> char[128] buf;
>> char[] line = buf[];
>> f.readln(line);
>> f.readln(line);
>> Which should not allocate at all in this case, and is completely safe if
>> it *does* have to allocate (like if some malicious code came along and
>> rewrote the file to have a 500-character first line).  Try to do *that*
>> with std::string :)
>> Man D is just so cool!
>> -Steve
>
> I actually have no idea whether this reallocates or not because of the  
> way the
> scarily complex readlnImpl() code works in std.stdio, and I think I was  
> the last
> person to modify that code.

Having had to understand it a bit because I just updated appender and it  
uses appender, I can assure you it only reallocates if it runs out of  
provided buffer space.

In fact, before my changes, I think it would have allocated.  I think  
actually, the second call will definitely reallocate if the first one  
did.  I think we may need to revisit readlnImpl.  It might be better if  
readln in general took an output range instead of a buffer.

-Steve