Python-Like enumerate() In C++17--Nathan Reed

By Adrien Hamelin | Nov 29, 2018 01:28 PM | Tags: intermediate community

Handy little piece of code.

Python-Like enumerate() In C++17

by Nathan Reed

From the article:

Python has a handy built-in function called enumerate(), which lets you iterate over an object (e.g. a list) and have access to both the index and the item in each iteration. You use it in a for loop, like this:

for i, thing in enumerate(listOfThings):
    print("The %dth thing is %s" % (i, thing))

Iterating over listOfThings directly would give you thing, but not i, and there are plenty of situations where you’d want both (looking up the index in another data structure, progress reports, error messages, generating output filenames, etc).

C++ range-based for loops work a lot like Python’s for loops. Can we implement an analogue of Python’s enumerate() in C++? We can!

AWS launches the C++ lambda runtime

By Blog Staff | Nov 29, 2018 12:49 PM | Tags: None

More C++ and the cloud:

Introducing the C++ Lambda Runtime

by Chris Munns

From the article:

Today, AWS Lambda announced the availability of the Runtime API. The Runtime API allows you to write your Lambda functions in any language, provided that you bundle it with your application artifact or as a Lambda layer that your application uses.

As an example of using this API and based on the customer demand, AWS is releasing a reference implementation of a C++ runtime for Lambda. This C++ runtime brings the simplicity and expressiveness of interpreted languages while maintaining the superiority of C++ performance and low memory footprint. These are benefits that align well with the event-driven, function-based, development model of Lambda applications...

Quick Q: Regarding shared_ptr reference count block

By Adrien Hamelin | Nov 28, 2018 12:03 PM | Tags: intermediate community

Quick A: it is an implementation detail for the std.

Recently on SO:

Regarding shared_ptr reference count block

(1) Regarding size: How can I programatically find the exact size of the control block for a std::shared_ptr?

There is no way. It's not directly accessible.

(2) Regarding logic: Additionally, boost::shared_ptr mentions that they are completely lock-free with respect to changes in the control block.(Starting with Boost release 1.33.0, shared_ptr uses a lock-free implementation on most common platforms.) I don't think std::shared_ptr follows the same - is this planned for any future C++ version? Doesn't this also mean that boost::shared_ptr is a better idea for multithreaded cases?

Absolutely not. Lock-free implementations are not always better than implementations that use locks. Having an additional constraint, at best, doesn't make the implementation worse but it cannot possibly make the implementation better.

Consider two equally competent programmers each doing their best to implement shared_ptr. One must produce a lock-free implementation. The other is completely free to use their best judgment. There is simply no way the one that must produce a lock-free implementation can produce a better implementation all other things being equal. At best, a lock-free implementation is best and they'll both produce one. At worse, on this platform a lock-free implementation has huge disadvantages and one implementer must use one. Yuck.

RangeOf: A better span--Corentin Jabot

By Adrien Hamelin | Nov 28, 2018 11:58 AM | Tags: intermediate experimental

Do you like span?

RangeOf: A better span

by Corentin Jabot

From the article:

I don’t like span.

Since that article was posted, the committee improved span quite a bit by removing operator== and making it’s size() consistent with that of vector after a lot of discussions. And I mean a lot...

Meeting C++ and Meeting Embedded trip report--Conan C/C++ Package Manager

By Adrien Hamelin | Nov 28, 2018 11:55 AM | Tags: community

Were you there? 

Meeting C++ and Meeting Embedded trip report

by Conan C/C++ Package Manager

From the article:

On Wednesday, before Meeting C++, we attended and presented a talk at Meeting Embedded, a new conference about many topics related to embedded systems. C++ and C had a relevant role in this conference, obviously (accordingly to Dan Saks statistics around 60% in embedded code is C, then around 20% is C++, followed by assembly), but where other topics presented, like Rust, protocols for embedded (MQTT), academic and professional education, real-time systems.

We did our own talk Continuous Integration of C/C++ for embedded and IoT with Jenkins, Docker and Conan, which went quite well, especially considering that we were running a real demo, live updating the embedded code in a Raspberry PI, that was built with Docker in Jenkins, using cross-compiled (from Windows) packages, and uploaded to Artifactory, all of that done in the live demo...

Quick Q: What does it mean to return a reference?

By Adrien Hamelin | Nov 27, 2018 02:10 PM | Tags: basics

Quick A: The returned variable can be modified.

Recently on SO:

What does it mean to return a reference?

It means you return by reference, which is, at least in this case, probably not desired. It basically means the returned value is an alias to whatever you returned from the function. Unless it's a persistent object it's illegal.

For example:

int& foo () {
    static int x = 0;
    return x;
}

//...
int main()
{
    foo() = 2;
    cout << foo();
}

would be legal and print out 2, because foo() = 2 modifies the actual value returned by foo.

However:

int& doit () {
    int x = 0;
    return x;
}

would be illegal (well, accessing the returned value would), because x is destroyed when the method exits, so you'd be left with a dangling reference.

Returning by reference isn't common for free functions, but it is for methods returning members. For example, in the std, the operator [] for common containers return by reference. For example, accessing a vector's elements with [i] returns an actual reference to that element, so v[i] = x actually changes that element.

Also, I hope that "is essentially equal to this code" means that they're semantically sort of (but not really) similar. Nothing more.

Inline Namespaces 101--Jonathan Müller

By Adrien Hamelin | Nov 27, 2018 01:58 PM | Tags: c++11 advanced

Obscure feature? Not for long.

Inline Namespaces 101

by Jonathan Müller

From the article:

Almost three years ago — wow, how time flies — I blogged about namespace aliases and called them one of C++ most underrated features (which probably was a bit of a click bait).

Let’s talk about some other namespace feature, that is, well, not quite underrated, but relatively obscure: inline namespace. They are namespaces that don’t really introduce a scope, except when they do.

So what can you do with them?

How to teach C++--Marius Elvert

By Adrien Hamelin | Nov 27, 2018 01:53 PM | Tags: community

Do you have a way?

How to teach C++

by Marius Elvert

From the article:

In the closing Keynote of this year’s Meeting C++, Nicolai Josuttis remarked how hard it can be to teach C++ with its ever expanding complexity. His example was teaching rookies about initialization in C++, i.e. whether to use assignment =, parens () or curly braces {}. He also asked for more application-level programmers to participate.

Well, I am an application programmer, and I also have experience with teaching C++. Last year I held a C++ introductory course for experienced C programmers who mostly had never used C++ before. From my experience, I can completely agree with what Nico had to say about teaching C++. The language and its subtlety can be truly overwhelming.

Most of the complexity in C++ boils down to tuning your code for optimal performance. We cannot just leave that out, can we? After all, the sole reason to use C++ is performance, right?

CLion 2018.3 released with remote dev support -- Anastasia Kazakova

By Anastasia Kazakova | Nov 27, 2018 12:20 PM | Tags: None

CLion has just got a huge update!!

How to Design Function Parameters That Make Interfaces Easier to Use (1/3)--Jonathan Boccara

By Adrien Hamelin | Nov 26, 2018 02:30 PM | Tags: intermediate community

Readability is important.

How to Design Function Parameters That Make Interfaces Easier to Use (1/3)

by Jonathan Boccara

From the article:

When you look at an function in an interface, 3 prominent things give you indications about how to use it: its name, its parameters and its return type. And when you look at a piece of code calling that function, it’s just its name and its function parameters.

We’ve already covered in details how to give good names to the components of your code. Now we’re going to examine how to design function parameters in a way that both your interfaces and the code that calls them are as expressive as can be.

Summed up in one sentence, you want to make the decision of what arguments to pass to your functions a no-brainer.

There are a lot of things to say about how to achieve this. So much so that you will find the contents broken down into 3 articles in order to make it easier to digest:

• Part 1: interface-level parameters, one-parameter functions, const parameters,
• Part 2: calling contexts, strong types, parameters order,
• Part 3: packing parameters, processes, levels of abstraction.

To support this series I’ve taken many examples from interfaces I’ve worked on, except that I’ve stripped out all domain aspects to make them both simpler and disclosable...