An implementation of generic lambdas is now available

For those interested in C++ standardization and not already following along at, here’s an item of likely interest:

An implementation of generic lambdas (request for feedback)—Faisal Vali

This week, Faisal Vali shared an initial “alpha” implementation of generic lambdas in Clang. Faisal is the lead author of the proposal (N3418), with Herb Sutter and Dave Abrahams.

To read and participate in the active discussion, see the message thread on std-proposals.

Here is a copy of Faisal’s announcement…

Read more at…


On yesterday’s thread, I just wrote in a comment:

@Jon: Yes, C++ is complex and the complexity is largely because of C compatibility. I agree with Bjarne that there’s a small language struggling to get out — I’ve participated in private experiments to specify such a language, and you can do it in well under half the complexity of C++ without losing the expressivity and flexibility of C++. However, it does require changes to syntax (mainly) and semantics (secondarily) that amount to making it a new language, which makes it a massive breaking change for programs (where existing code doesn’t compile and would need to be rewritten manually or with a tool) and programmers (where existing developers need retraining). That’s a very big tradeoff. So just as C++ ‘won’ in the 90s because of its own strengths plus its C compatibility, C++11 is being adopted because of its own strengths plus its C++98 compatibility. At the end of the day compatibility continues to be a very strong force and advantage that isn’t lightly tossed aside to “improve” things. However, it’s still worthwhile and some interesting things may come of it. Stay tuned, but expect (possible) news in years rather than months.

That reminded me of a snippet from the September 2012 issues of CACM. When I first read it, I thought it was so worthwhile that I made a magnified copy and pasted it on the window outside my office at work – it’s still there. The lightly annotated conclusion is shown here.

imageThe article itself was about a different technology, but the Lessons Learned conclusion remind us of the paramount importance of two things:

  • Backward compatibility with simple migration path (“compat”). That’s what keeps you “in the ecosystem.” If you don’t have such compatibility, don’t expect wide adoption unless there are hugely compelling reasons to put up with the breaking change. It’s roughly the same kind of ecosystem change for programmers to go from Language X to Language Y as for users to go from Platform X to Platform Y (e.g., Windows to Mac, iPhone to Android) – in each case you have a lot of relearning, and you lose understood tools and services some of which have replacements and some of which don’t.
  • Focusing on complete end-to-end solutions (“SFE” or scenario-focused engineering). This is why it’s important not to ship just a bunch of individual features, because that can leave holes where Steps 1, 2, and 4 of an end-to-end experience are wonderful but Step 3 is awkward, unreliable, or incomplete, which renders much of the good work in the other steps unuseful since they can’t be used as much or possibly at all.


Perspective: “Why C++ Is Not ‘Back’”

John Sonmez wrote a nice article on the weekend – both the article and the comments are worth reading.

“Why C++ Is Not ‘Back’”

by John Sonmez

I love C++. […] There are plenty of excellent developers I know today that still use C++ and teach others how to use it and there is nothing at all wrong with that.

So what is the problem then?

[…] Everyone keeps asking me if they need to learn C++, but just like my answer was a few years ago, it is the same today—NO!

Ok, so “NO” in caps is a bit harsh.  A better answer is “why?”


Although I don’t agree with everything John says, he presents something quite valuable, and unfortunately rare: a thoughtful hype-free opinion. This is valuable especially when (not just “even when”) it differs from your own opinion, because combining different thoughtful views of the same thing gives something exceedingly important and precious: perspective.

By definition, depth perception is something you get from seeing and combining more than one point of view. This is why one of my favorite parts of any conference or group interview is discussions between experts on points where they disagree – because experts do regularly disagree, and when they each present their thoughtful reasons and qualifications and specific cases (not just hype), you get to see why a point is valid, when it is valid and not valid, how it applies to a specific situation or doesn’t, and so on.

I encourage you to read the article and the comments. This quote isn’t the only thing I don’t fully agree with, but it’s the one thing I’ll respond to a little from the article:

There are only about three sensible reasons to learn C++ today that I can think of.

There are other major reasons in addition to those, such as:

  • Servicing, which is harder when you depend on a runtime.
  • Testing, since you lose the ability to test your entire application (compare doing all-static or mostly-static linking with having your application often be compiled/jitted for the first time on an end user’s machine).

These aren’t bad things in themselves, just tradeoffs and reasons to prefer native code vs managed code depending on your application’s needs.

But even the three points John does mention are very broad reasons that apply often, especially the issue of control over memory layouts, to the point where I would say: In any language, if you are serious about performance you will be using arrays a lot (not “always,” just “a lot”). Some languages make that easier and give you much better control over layout in general and arrays in particular, while other languages/environments make it harder (possible! but harder) and you have to “opt out” or “work against” the language’s/runtime’s strong preference for pointer-chasing node-based data structures.

For more, please see also my April 2012 Lang.NEXT talk “(Not Your Father’s) C++”, especially the second half:

  • From 19:20, I try to contrast the value and tenets of C++ and of managed language/environments, including that each is making a legitimate and useful design choice.
  • From 36:00, I try to address the question of: “can managed languages do essentially everything that’s interesting, so native C/C++ code should be really just for things like device drivers?”
  • From 39:00, I talk about when each one is valuable and should be used, especially that if programmer time is your biggest cost, that’s what you should optimize for and it’s exactly what managed languages/environments are designed for.

But again, I encourage you to read John’s article – and the comments – yourself. There’s an unusually high signal-to-noise ratio here.

It’s always nice to encounter a thoughtful balanced piece of writing, whether or not we agree with every detail. Thanks, John!