How to Make SFINAE Pretty – Part 1: What SFINAE Brings to Code

By Adrien Hamelin | May 21, 2018 12:16 PM | Tags: advanced

New series!

How to Make SFINAE Pretty – Part 1: What SFINAE Brings to Code

by Jonathan Boccara

From the article:

SFINAE is a bit like a windmill. It sits as a wart in the middle of an interface, BUT it’s useful to create elaborate static polymorphism, in particular before C++17 and if constexpr, and even in some use cases in C++17.

I thought we had to live with this tradeoff, until I watched a talk from Stephen Dewhurst at CppCon. In this inspring talk, Stephen shows how to turn SFINAE around to make it very expressive in an interface. Watching this talk changed my way of coding template interfaces...

Default-constructibility is overrated--Arthur O’Dwyer

By Adrien Hamelin | May 18, 2018 11:19 AM | Tags: community advanced

What do you think?

Default-constructibility is overrated

by Arthur O’Dwyer

From the article:

The Ranges Technical Specification includes very many concept definitions (based on the Concepts TS), including for example Integral and Predicate. It also provides a concept named Regular which implements a variation on the “Regular” concept described by Alexander Stepanov in his paper '’Fundamentals of Generic Programming’’ (1998)...

Quick Q: Undefined behavior and sequence points

By Adrien Hamelin | May 10, 2018 11:48 AM | Tags: advanced

Quick A: No quick A.

Recently on SO:

Undefined behavior and sequence points

What are "sequence points"?

What is the relation between undefined behaviour and sequence points?

I often use funny and convoluted expressions like a[++i] = i;, to make myself feel better. Why should I stop using them?

If you've read this, be sure to visit the follow-up question Undefined behavior and sequence points reloaded.

(Note: This is meant to be an entry to Stack Overflow's C++ FAQ. If you want to critique the idea of providing an FAQ in this form, then the posting on meta that started all this would be the place to do that. Answers to that question are monitored in the C++ chatroom, where the FAQ idea started out in the first place, so your answer is very likely to get read by those who came up with the idea.)

‘Speedy Gonzales’ Serializing (Re)Actors via Allocators--"No Bugs" Hare

By Adrien Hamelin | May 8, 2018 12:33 PM | Tags: advanced

Actors.

‘Speedy Gonzales’ Serializing (Re)Actors via Allocators

by "No Bugs" Hare

From the article:

As we briefly discussed in Part I of this mini-series [NoBugs17a], message-passing technologies such as (Re)Actors (a.k.a. Actors, Reactors, ad hoc FSMs, and event-driven programs) have numerous advantages – ranging from being debuggable (including post-factum production debugging), to providing better overall performance.

In [NoBugs17a] and [NoBugs17b], we discussed an approach to handling allocations for (Re)Actors, and then were able to achieve a safe dialect of C++ (that is, as long as we’re following a set of well-defined local rules). Now, let’s take a look at another task which can be facilitated by per-(Re)Actor allocators – specifically, at the task of serializing (Re)Actors that are later going to be de-serialized by the same executable. While one solution for this task was provided in [Ignatchenko-Ivanchykhin16], the proposed ‘ultra-fast’ serialization is rather cumbersome to maintain, and in most cases it can be beaten performance-wise by serializing at the allocator level...

Without form and void--Barry Revzin

By Adrien Hamelin | May 7, 2018 12:53 PM | Tags: advanced

Did you encounter the problem?

Without form and void

by Barry Revzin

From the article:

In C++, void is a pretty strange thing. We can cast expressions to void, throw-expressions have void type, void* can point to anything, and void functions can actually return back to the caller. But we can’t have objects of type void or even write a type like void&. A function declaration like void f(void) is actually a nullary function. It’s a bit weird — but it’s not something a lot of people lose sleep over.

Until it starts wreaking havoc on your generic code — because it’s like the vector<bool> of the type system...

[[trivial_abi]] 101--Arthur O’Dwyer

By Adrien Hamelin | May 7, 2018 12:41 PM | Tags: community advanced

Interesting!

[[trivial_abi]] 101

by Arthur O’Dwyer

From the article:

Finally, a blog post on [[trivial_abi]]!

This is a brand-new feature in Clang trunk, new as of about February 2018. It is a vendor extension to the C++ language — it is not standard C++, it isn’t supported by GCC trunk, and there is no active WG21 proposal to add it to the standard C++ language, as far as I know...

"Modern C++ Template Programming" with Nicolai Josuttis

By Meeting C++ | May 2, 2018 02:19 AM | Tags: workshop training templates meetingcpp intermediate c++17 c++14 c++11 advanced

Meeting C++ 2018 offers also a workshop with Nicolai Josuttis:

Modern C++ Template Programming

by Jens Weller

From the article:

Each and every C++ programmer uses templates. Containers such as vector<> or array<>, strings, algorithms such as sort(), iterators, and I/O streams are all implemented as generic code. Modern C++ adds type traits, smart pointers, and template member functions such as emplace(), and generic lambdas as a tricky form of generic code.

Nevertheless the knowledge and understanding of how to implement and use templates is very limited and each and every programmer is sooner or later getting uncertain.

This workshop therefore discusses templates for a whole day to make clear what it means to use templates and how to use them in practice. As a result the general understanding of templates will be improved and generic code might become more helpful and less surprising.

Quick Q: int a[] = {1,2,}; Weird comma allowed. Any particular reason?

By Adrien Hamelin | Apr 20, 2018 12:29 PM | Tags: advanced

Quick A: For convenience.

Recently on SO:

int a[] = {1,2,}; Weird comma allowed. Any particular reason?

It makes it easier to generate source code, and also to write code which can be easily extended at a later date. Consider what's required to add an extra entry to:

int a[] = {
   1,
   2,
   3
};

... you have to add the comma to the existing line and add a new line. Compare that with the case where the three already has a comma after it, where you just have to add a line. Likewise if you want to remove a line you can do so without worrying about whether it's the last line or not, and you can reorder lines without fiddling about with commas. Basically it means there's a uniformity in how you treat the lines.

Now think about generating code. Something like (pseudo-code):

output("int a[] = {");
for (int i = 0; i < items.length; i++) {
    output("%s, ", items[i]);
}
output("};");

No need to worry about whether the current item you're writing out is the first or the last. Much simpler.

Contra built-in library types--Arthur O’Dwyer

By Adrien Hamelin | Apr 17, 2018 12:18 PM | Tags: advanced

What is your opinion?

Contra built-in library types

by Arthur O’Dwyer

From the article:

C++ has several guiding principles or mantras. The most famous one is probably “zero-cost abstraction,” but for my money the most important one is “C++ does not have a string type.”

uninitialized_tag in C++--Marius Elvert

By Adrien Hamelin | Apr 17, 2018 12:17 PM | Tags: performance advanced

Optimise or not?

uninitialized_tag in C++

by Marius Elvert

From the article:

No doubt, C++ is one of those languages you can use to squeeze out every last drop of your CPU’s processing power. On the other hand, it also allows a high amount of abstraction. However, micro-optimization seldom works well with nice abstractions...