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Template meta-functions for detecting template instantiation--Ivan Čukić

By Adrien Hamelin | Mar 19, 2019 11:44 AM | Tags: c++17 advanced

Templates are great.

Template meta-functions for detecting template instantiation

by Ivan Čukić

From the article:

I’ve been playing around with type meta-tagging for my Voy reactive streams library (more on that some other time) and realized how useful it is to be able to check whether a given type is an instantiation of some class template, so I decided to write a short post about it...

A gentle introduction to jump threading optimizations--Aldy Hernandez

By Adrien Hamelin | Mar 18, 2019 10:50 AM | Tags: performance advanced

Your complier does magic.

A gentle introduction to jump threading optimizations

by Aldy Hernandez

From the article:

As part of the GCC developers‘ on-demand range work for GCC 10, I’ve been playing with improving the backward jump threader so it can thread paths that are range-dependent. This, in turn, had me looking at the jump threader, which is a part of the compiler I’ve been carefully avoiding for years. If, like me, you’re curious about compiler optimizations, but are jump-threading-agnostic, perhaps you’ll be interested in this short introduction...

Quick Q: Pointer to class data member “::*”

By Adrien Hamelin | Mar 13, 2019 12:53 PM | Tags: advanced

Quick A: a pointer that lets you access the value of the member of an instance.

Recently on SO:

Pointer to class data member “::*”

It's a "pointer to member" - the following code illustrates its use:

#include <iostream>
using namespace std;

class Car
{
    public:
    int speed;
};

int main()
{
    int Car::*pSpeed = &Car::speed;

    Car c1;
    c1.speed = 1;       // direct access
    cout << "speed is " << c1.speed << endl;
    c1.*pSpeed = 2;     // access via pointer to member
    cout << "speed is " << c1.speed << endl;
    return 0;
}

As to why you would want to do that, well it gives you another level of indirection that can solve some tricky problems. But to be honest, I've never had to use them in my own code.

Edit: I can't think off-hand of a convincing use for pointers to member data. Pointer to member functions can be used in pluggable architectures, but once again producing an example in a small space defeats me. The following is my best (untested) try - an Apply function that would do some pre &post processing before applying a user-selected member function to an object:

void Apply( SomeClass * c, void (SomeClass::*func)() ) {
    // do hefty pre-call processing
    (c->*func)();  // call user specified function
    // do hefty post-call processing
}

The parentheses around c->*func are necessary because the ->* operator has lower precedence than the function call operator.

Understanding C++ Modules: Part 1: Hello Modules, and Module Units--Colby Pike

By Adrien Hamelin | Mar 12, 2019 12:04 PM | Tags: experimental advanced

Complex, but useful!

Understanding C++ Modules: Part 1: Hello Modules, and Module Units

by Colby Pike

From the article:

My previous posts on modules have received a lot of attention. I’m happy that I’ve been able to kick-start a lot of conversation, but I’ve also seen that a large part of the community is still unclear on what modules actually are.

There is a lot of ground to cover. I can’t do it all in one sitting, and I doubt you’d want to read the entire thing in one go. I’ll be breaking this up, starting at the most high-level aspects and drilling down over time. I intend these posts will clarify and discuss what modules are, what they can do, and what they are intended to do, what they cannot do, and how they are used...

2 Lines Of Code and 3 C++17 Features - The overload Pattern--Bartlomiej Filipek

By Adrien Hamelin | Feb 18, 2019 11:26 AM | Tags: c++17 advanced

Proof that you can do more!

2 Lines Of Code and 3 C++17 Features - The overload Pattern

by Bartlomiej Filipek

From the article:

While I was doing research for my book and blog posts about C++17 several times I stumbled upon this pattern for visitation of std::variant:

template<class... Ts> struct overload : Ts... { using Ts::operator()...; };
template<class... Ts> overload(Ts...) -> overload<Ts...>;

std::variant<int, float> intFloat { 0.0f };
std::visit(overload(
    [](const int& i) { ... },
    [](const float& f) { ... },
  ),
  intFloat;
);

With the above pattern, you can provide separate lambdas “in-place” for visitation.

It’s just two lines of compact C++ code, but it packs a few interesting concepts.

Let’s see how this thing works and go through the three new C++17 features that enable this one by one.