Neal Stephenson has it wrong

For noreason I can identify I suddenly noticed something today:

They're called "emojis", not "mediaglyphics".

Of course, he pretty much nailed everything except the name.

Yeah, well, you know, that’s just, like, your workflow, man.

I caught some flack at work this week: I circulated an early draft of a document that I was struggling with in plain text¹ and my boss was very clear that he wanted me to use Word in the future so there would be change tracking and out-of-band comments. On the plus side those remarks came packaged up with some useful suggestions for the piece.

Once I tamped down my reflexive defensiveness and the basic anxiety that comes with screwing up at work, I pulled up my big kid underwear and moved on. Then, having decided to be an adult about this, I ran smack dab into a counter example for $BOSS's point. I received a second set of highly useful changes in the same document. Conflicting changes. I'm not aware of any good tooling to handle conflicting changes in Word, but it was no problem for me to handle the conflicts in my text document: I just opened the files in my favorite visual merge tool.² and got on with it.

Caveat time. To take the "plain text means we can use good tools" thing seriously we'd want to put all our draft work in VC repositories, and when that occurred to me my first reaction was "Who'd want to do that?" I mean, yeah that makes sense for major pieces of writing, but it's not obvious that you want to maintain a full history on every minor document you bang out day in and day out.

But then I had another thought...

Caveat on the caveat. Which was "Hey, how do people who are really committed to Word deal with the possibility of conflicting changes, anyway?" A little poking around the web suggest that my employer's answer is completely mainstream. At the management tier we put everything in SharePoint and let it enforce serialized editing, so they're already putting all their work in a repository. Maybe the whole idea isn't so silly after all.

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¹ Now, I would never send plain text to the clients, but I often do my initial composition in text because the sense of informality helps me feel safe trying out different formulations in search of a natural arc through complex subjects.

² Meld as it happens. But not because I've tried all the options: it was just the first one I spent any time with and it's been consistently available.

Algorithms header knowledge check

Note some late additions marked with ^*.

^* After posting this I began to feel it needed a little bit more detail. And then that it needed quite a bit more detail.

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The C++ standard library's algorithm header has a routine sutiable for counting the number of places of disagreement between two equal sized collections of elements. What's it called? Hint: it's not called "count_differences". ^*Nor is it called count_if (unless you happen to be using C++-23 because count_if doesn't have an overload for parallel containers.⁰) My work projects are in C++-17 and my home projects in'17 or '20.

Answer

inner_product

^*One approach is to write a "sum" function that adds just as in the usual inner product, but the make the one that would do element multiplication in the standard inner produt return zero when the two values are equal and one if they differ.

For that matter, what educational backgrounds would prepare you to recognize that as the routine you want?¹ How does this compare to Kate Gregory's story about partial_sort_copy and how it would be better called top_n?

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^*0 C++23 doesn't introduce a parallel overload either, but it does introduce zip_view and zip which will allow you to efficiently produce on single container of apparent pairs from the parallel containers. Then you can use the single-container version of count_if. Obvious. Right?

¹ My combination of physics and prior experience with the algorithm header's love affair with having a user-supplied-predicate-to-change-the-behavior overload meant that I spotted it as soon as I read the name, but ... that's a rather esoteric requirement for user's to know what they're seeing.

Voice-assistant fails

Accumulated over the years, but I got another one the other day that triggered me.

Me:

[Navigating to a business in the US sowthwqest]

Creppy voice assistant (CVA):

In five-hundred feet, turn left on El Camino Real Street¹.

Me:

[::Sighs::]

CVA:

[Interrupts a conversation in the car]

Me:

Hold your horse, [CVA].

CVA:

[Starts reading the Wikipeia article on the idiom]

Me:

[CVA], play 2112.

CVA:

Now playing two-thousand-one-hundred-twelve.

Me:

[::Fumes:: until the music sweeps me away]

It's all about context seneitivity. Or the lack thereof.

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¹ With "Real" pronounced as a single sylable. Of course.

Career opportunity

Desperately seaking a licensned professional to tell us that we're making good parenting choices.

Bringing C Structs into the C++ Lifetime Model

In addition to legacy code in our own projects, I sometimes "get" to work against libraries (legacy or modern written in plain C. Which is OK. I learned C a long time ago and I'm not intimidated by it, though it can take a while to get back into the right mindset. Of course, there are things I miss. Static polymorphism and namespaces, for instance, are pretty small conceptual changes with significant convenience factor for the programmer.¹

Now, C++ has a reputation as being a dangerous language where it is easy write really broken code. That impression is not wrong, but it is incomplete: the lagnuage also offers features that support writing code that has enforced safety in some aspects. It's not trivial and it takes both discipline and some understanding of how the features work, but in my opinion it takes less discipline to write memory-safe C++ code than memory-safe C code.²

This article covers one way to bring a C struct into the C++ lifetime model to leverage the better (or at least more automatic) memory safety of C++ library primitives.

We start with a highly artificial example struct designed to be a pain memory wise:³

 struct thing {
    int i;
    double d;
    char *s
    int *ary;
};

Each of the pointers pose us some (interrelated) questions:

• Where do the objects that will be pointed to live? Heap? Stack? Data segment? Global memory? Memory mapped file? Something really exotic?
• How do we ensure that the pointer is not used after the objects go away (if they go away)?
• If they exist on the free-store, how do control deallocation?

The questions aren't unique to C, they are the same ones that must always be dealt with. But C code deals with them all every time, while other languages may have built-in answers to some of them.⁴

Nor can you necessarily answer the questions by static examination of the code, but in the case I faced at work, both pointers were consistently pointing at dynamically allocated objects. Moreover the number we needed could not be determined at compile time, so we were storing the thing *'s in a vector.

We had an existing C function thing *newThing(size_t array_size, const char *label) which would create a new struct thing on the heap (with a alloc family function), set default values of i and d, set the string and allocate (but not populate) the array and return the pointer to the thing. This is analogous to a C++ constructor, but for some reason (history, no doubt) we were handling the three calls to free manually each time we needed to reap one of these things.

Then we did something roughly like this:

{
    std::vector<const thing*> thing_list;
    for (const auto &input : inputs)
        list.push_back(newThing(input.name, input.size()));
    process_list(thing_list);
}

Which, of course, loses three heap allocated objects for every item in the inputs container.

Replicating a proper, but C-like, approach to memory management here would mean writing a destructor-analog (perhaps void reapThing(thing *p)) as a free function and inserting std::for_each(thing_list.begin(), thing_list.end(), reapThing); before the closing brace. That works and I wouldn't be displeased to see it in a legacy project like the one I'm working on, but I think we can do a little better.

The "doing better" interface is actually quite simple:⁵

#include "thing.h"

struct thing_wrapper : public thing
{
    thing_wrapper();
    thing_wrapper(size_t array_size, std:string_view label);
    thing_wrapper(const thing_wrapper &);
    ~thing_wrapper();
    
    thing_wrapper &operator=(const string_wrapper &);
}

The wrapper has the same data, but manages the sub-allocations for you. What complexity there is lies in ensuring that the constructors, assignment operators and destructor all agree on memory management of the sub-allocations.⁶ You might also want to add a constructor and assignment operator taking a const thing &, but this is a leap of faith insofar as nothing will enforce a consistent allocation strategy on those inputs. Similarly you can consider supporting move operations if you have a particular use for them.

With the wrapper in place we can change the original code to something like:

{
    std::vector<std::unique_ptr<const thing>> thing_list;
    for (const auto &input : inputs)
        list.emplace_back(std::make_unique<thing_wrapper>(input.name, input.size()));
    process_list(thing_list);
}

With no need, now, for explicit clean-up code.

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¹ Oddly, neither of these is trivial to add because they imperil the universal linkability of C (which depends on not needing a vendor-dependent name-mangling scheme).

² At the foundational level, it is the object lifetime model that supports this, and at the practical level it is exploited in the standard library which offers a more powerful set of primitives than the C standard library. Step one for writing a robust C program at scale is to get a more robust library (which you might be able to get off the shelf or might want to write yourself).

³ It is, however, analogous to the problem I faced at work today.

⁴ Many "managed" languages have everything on the free-store, and use a garbage collector to resolve the lifetime question.

⁵ I've chosen to make this a struct rather than a class for two reasons. First because the whole interface we want to derive is public: we're not going to extend thing in any way beyond supporting the C++ lifetime model. Second because of Core Guideline C2: the C code enforces no invariant so we don't add one.

⁶ The safe thing to do, is use the facilities used by the code that provides the underlying structure, which in the case of pure c libraries usually means *alloc/free or some wrapper around the same. You may be able to defer to any pre-existing C functions that perform the set-up and tear-down.