A commenter asked:
thread_local X tlsX; ??
Herb, I hope you aren’t backtracking on Hungarian Notation now that you work for Microsoft. Say it aint so…
It ain’t so. Besides, Microsoft’s Framework Developer’s Guide prominently intones: “Do not use Hungarian notation.”
Warts like “tls” and “i” are about lifetime and usage, not type. Here “tls” denotes that each thread gets its own copy of the value that is constructed and destroyed once per thread that uses it (lifetime) and doesn’t need to be synchronized using mutexes (usage). As another example of usage warts, I’ll also use “i” for a variable that’s used as an index or for iteration — and given that the “i” convention goes back to before BASIC, we shouldn’t try to pin the Hungarian tail on that donkey.
Having said that, though, many people have variously decried and defended different forms of Hungarian, and you may notice a pattern… they’re mostly:
- decrying Systems Hungarian, the wildly popularized version which focuses on encoding the type, and
- defending Applications Hungarian, the originally described version which focuses on encoding the usage.
Today, “Hungarian” nearly always means Systems Hungarian. The main trouble with Systems Hungarian comes from trying to embed information about a variable’s type into the variable’s name by prepending an encoded wart like the venerable sz, pach, ul, and their ilk. Although potentially helpful in a weakly-typed language like C, that’s known to be brittle and the prefixes tend to turn into lies as variable types morph during maintenance. The warting systems also don’t extend well to user-defined types and templates.
I’ve railed against the limitations and perils of Hungarian with Andrei Alexandrescu in our book C++ Coding Standards, where I made sure it was stated right up front as part of “Item 0: Don’t sweat the small stuff (or, Know what not to standardize)”:
Example 3: Hungarian notation. Notations that incorporate type information in variable names have mixed utility in type-unsafe languages (notably C), are possible but have no benefits (only drawbacks) in object-oriented languages, and are impossible in generic programming. Therefore, no C++ coding standard should require Hungarian notation, though a C++ coding standard might legitimately choose to ban it.
and with Jim Hyslop in our article “Hungarian wartHogs”:
“… the compiler already knows much more than you do about an object’s type. Changing the variable’s name to embed type information adds little value and is in fact brittle. And if there ever was reason to use some Hungarian notation in C-style languages, which is debatable, there certainly remains no value when using type-safe languages.”
There’s an amusing real-world note later in that article. I’ll pick up where the Guru is saying:
“I recall only one time when Hungarian notation was useful on a project. … One of the programmers on the project was named Paul,” the Guru explained. “Several months into the project, while still struggling to grow a ponytail and build his report-writing module, he pointed out that Hungarian notation had helped him find a sense of identity, for he now knew what he was…” She paused.
I blinked. It took me about ten seconds, and then I shut my eyes and grimaced painfully. “Pointer to array of unsigned long,” I groaned.
She smiled, enjoying my pain. “True story,” she said.
It is indeed a true story. I worked with him in 1993. The joke was bad then, too, but at least using Hungarian was more defensible because the project’s code was written in C. I found it handy at the time, but now that I work in more strongly typed languages I find the type-embedding version of Hungarian more actively harmful than actually useful.
You might call me a Hungarian emigrant, now living happily as an expat out in eastern C++ near the Isle of Managed Languages.