Technical Difficulties from on Top of the Mountain
2013-09-02
  Cleaning up the C++ past.
Once apon a time, I bought a C++ library. Shocking I know, people thought they could make money selling libraries. Most people have gotten over that misconception.

But I didn't buy it to use it, I bought it to learn from. I had written my own cross platform networking library which ran on SunOS, HPUX, SGI IRIX, Ultrix, BSD and Windows NT; and it worked really well. But I was now slowly delving into threading and didn't want to suffer through same five year learning curve as I had with networking. I had scratched the surface of pthreads, and I figured if I could get a Rosetta stone, I'd be most of the way there. So several hundred dollars later, I had the Object Space C++ cross platform libraries in my hands.

Their code for threads was great, because windows gives you a lot of high level calls while pthreads was basically parts; and it showed how you could make the windows things out of the pthread parts. But there was more on the CD besides this. There were these strange template things called Containers and Algorithms. These things warped my brain the way Flatland does the first time you read it, and for ten minutes you can visualize four dimensions in your head. But like my grasp of the thermal cycle of a propane refrigerator, after a night of rest, it was gone.

Some time down the road, I was ready to come back to Algorithms, and started off trying to do this:

void  someclass::somemethod(int x)
{
  struct { bool operator(something * ptr) { return ptr->sometest( x ) ; } } anon_test ;
  something * foundptr = stl::find_if( somelist.begin(), somelist.end(), anon_test) ;
}
This didn't work for all kinds of reasons, but even when I knocked down the easy ones (like creating local storage in the struct for x), I ended up hitting language limits like not being able to have an un-named struct, and I abandoned the whole thing.

There were really ugly work-arounds involving horrible bind macros and worse types so that just to compare a list of ints against x, you'd end up doing something like:

  binder2nd testor = bind2nd( greater(), x) ;
Ick. Wasn't going to happen, and for the most part, didn't. Not one project, or company I worked at in the next 15 years ever used STL containers, or algorithms. I'm sure somewhere, somebody used it, but I never ran into it.

Thankfully, the standards body took up all the patchwork that boost had been doing for ten years, and cleaned up C++ to make things easier and better. We got lambdas, closures, and a lot of duct tape like auto and range-for.

So now I can do my previous example in a much cleaner way, and even better, its readable:

void someclass::somemethod( int x)
{
  something * foundptr= std::find_if( somelist.begin(), somelist.end(), [x](something * ptr){ return ptr->sometest( x) ; } ) ;
}
The worst part of this is the little magic: [x] but you can go read about lambda syntax and you'll get it. And for performance, if you're going to use that predicate a lot, you can save it away ahead of time with just a tad more effort:
  auto xtest = [x](something * ptr){ return ptr->sometest( x) ; } ;
I think this is big.

Labels: , ,

 
Comments: Post a Comment

<< Home
Life in the middle of nowhere, remote programming to try and support it, startups, children, and some tinkering when I get a chance.

ARCHIVES
January 2004 / February 2004 / March 2004 / April 2004 / May 2004 / June 2004 / July 2004 / August 2004 / September 2004 / October 2004 / November 2004 / December 2004 / January 2005 / February 2005 / March 2005 / April 2005 / May 2005 / June 2005 / July 2005 / August 2005 / September 2005 / October 2005 / November 2005 / December 2005 / January 2006 / February 2006 / March 2006 / April 2006 / May 2006 / June 2006 / July 2006 / August 2006 / September 2006 / October 2006 / November 2006 / December 2006 / January 2007 / February 2007 / March 2007 / April 2007 / June 2007 / July 2007 / August 2007 / September 2007 / October 2007 / November 2007 / December 2007 / January 2008 / May 2008 / June 2008 / August 2008 / February 2009 / August 2009 / February 2010 / February 2011 / March 2011 / October 2011 / March 2012 / July 2013 / August 2013 / September 2013 / October 2013 / November 2013 / December 2013 / December 2014 / February 2015 / March 2015 / July 2016 / September 2016 / December 2016 / April 2017 / June 2017 /


Blogroll
Paul Graham's Essays
You may not want to write in Lisp, but his advise on software, life and business is always worth listening to.
How to save the world
Dave Pollard working on changing the world .. one partially baked idea at a time.
SnowDeal
Eric Snowdeal IV - born 15 weeks too soon, now living a normal baby life.
Land and Hold Short
The life of a pilot.

The best of?
Jan '04
The second best villain of all times.

Feb '04
Oops I dropped by satellite.
New Jets create excitement in the air.
The audience is not listening.

Mar '04
Neat chemicals you don't want to mess with.
The Lack of Practise Effect

Apr '04
Scramjets take to the air
Doing dangerous things in the fire.
The Real Way to get a job

May '04
Checking out cool tools (with the kids)
A master geek (Ink Tank flashback)
How to play with your kids

Powered by Blogger