The New Hacker's Dictionary

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1. [common] A good property or behavior (as of a program). Whether it was intended or not is immaterial. 2. [common] An intended property or behavior (as of a program). Whether it is good or not is immaterial (but if bad, it is also a [4981]misfeature). 3. A surprising property or behavior; in particular, one that is purposely inconsistent because it works better that way -- such an inconsistency is therefore a [4982]feature and not a [4983]bug. This kind of feature is sometimes called a [4984]miswart; see that entry for a classic example. 4. A property or behavior that is gratuitous or unnecessary, though perhaps also impressive or cute. For example, one feature of Common LISP's format function is the ability to print numbers in two different Roman-numeral formats (see [4985]bells whistles and gongs). 5. A property or behavior that was put in to help someone else but that happens to be in your way. 6. [common] A bug that has been documented. To call something a feature sometimes means the author of the program did not consider the particular case, and that the program responded in a way that was unexpected but not strictly incorrect. A standard joke is that a bug can be turned into a [4986]feature simply by documenting it (then theoretically no one can complain about it because it's in the manual), or even by simply declaring it to be good. "That's not a bug, that's a feature!" is a common catchphrase. See also [4987]feetch feetch, [4988]creeping featurism, [4989]wart, [4990]green lightning.

The relationship among bugs, features, misfeatures, warts, and miswarts might be clarified by the following hypothetical exchange between two hackers on an airliner:

A:"This seat doesn't recline."

B:"That's not a bug, that's a feature. There is an emergency exit door built around the window behind you, and the route has to be kept clear."

A:"Oh. Then it's a misfeature; they should have increased the spacing between rows here."

B:"Yes. But if they'd increased spacing in only one section it would have been a wart -- they would've had to make nonstandard-length ceiling panels

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to fit over the displaced seats."

A:"A miswart, actually. If they increased spacing throughout they'd lose several rows and a chunk out of the profit margin. So unequal spacing would actually be the Right Thing."

B:"Indeed."

`Undocumented feature' is a common, allegedly humorous euphemism for a [4991]bug. There's a related joke that is sometimes referred to as the "one-question geek test". You say to someone "I saw a Volkswagen Beetle today with a vanity license plate that read FEATURE". If he/she laughs, he/she is a geek (see [4992]computer geek, sense 2).

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feature creature n.

[poss. fr. slang `creature feature' for a horror movie] 1. One who loves to add features to designs or programs, perhaps at the expense of coherence, concision, or [4996]taste. 2. Alternately, a mythical being that induces otherwise rational programmers to perpetrate such crocks. See also [4997]feeping creaturism, [4998]creeping featurism.

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feature creep n.

[common] The result of [5002]creeping featurism, as in "Emacs has a bad case of feature creep".

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feature shock n.

[from Alvin Toffler's book title "Future Shock"] A user's (or programmer's!) confusion when confronted with a package that has too many features and poor introductory material.

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featurectomy /fee`ch*r-ek't*-mee/ n.

The act of removing a feature from a program. Featurectomies come in two flavors, the `righteous' and the `reluctant'. Righteous featurectomies are performed because the remover believes the program would be more elegant without the feature, or there is already an equivalent and better way to achieve the same end. (Doing so is not quite the same thing as removing a [5013]misfeature.) Reluctant featurectomies are performed to satisfy some external constraint such as code size or execution speed.

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feep /feep/

1. n. The soft electronic `bell' sound of a display terminal (except for a VT-52); a beep (in fact, the microcomputer world seems to prefer [5017]beep). 2. vi. To cause the display to make a feep sound. ASR-33s (the original TTYs) do not feep; they have mechanical bells that ring. Alternate forms: [5018]beep, `bleep', or just about anything suitably

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onomatopoeic. (Jeff MacNelly, in his comic strip "Shoe", uses the word `eep' for sounds made by computer terminals and video games; this is perhaps the closest written approximation yet.) The term `breedle' was sometimes heard at SAIL, where the terminal bleepers are not particularly soft (they sound more like the musical equivalent of a raspberry or Bronx cheer; for a close approximation, imagine the sound of a Star Trek communicator's beep lasting for five seconds). The `feeper' on a VT-52 has been compared to the sound of a '52 Chevy stripping its gears. See also [5019]ding.

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feeper /fee'pr/ n.

The device in a terminal or workstation (usually a loudspeaker of some kind) that makes the [5023]feep sound.

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feeping creature n.

[from [5027]feeping creaturism] An unnecessary feature; a bit of [5028]chrome that, in the speaker's judgment, is the camel's nose for a whole horde of new features.

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feeping creaturism /fee'ping kree`ch*r-izm/ n.

A deliberate spoonerism for [5032]creeping featurism, meant to imply that the system or program in question has become a misshapen creature of hacks. This term isn't really well defined, but it sounds so neat that most hackers have said or heard it. It is probably reinforced by an image of terminals prowling about in the dark making their customary noises.

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feetch feetch /feech feech/ interj.

If someone tells you about some new improvement to a program, you might respond: "Feetch, feetch!" The meaning of this depends critically on vocal inflection. With enthusiasm, it means something like "Boy, that's great! What a great hack!" Grudgingly or with obvious doubt, it means "I don't know; it sounds like just one more unnecessary and complicated thing". With a tone of resignation, it means, "Well, I'd rather keep it simple, but I suppose it has to be done".

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fence n. 1.

A sequence of one or more distinguished ([5039]out-of-band) characters (or other data items), used to delimit a piece of data intended to be treated as a unit (the computer-science literature calls this a `sentinel'). The NUL (ASCII 0000000) character that terminates strings in C is a fence. Hex FF is also (though slightly less frequently) used this way. See [5040]zigamorph. 2. An extra data value inserted in an array or other data

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structure in order to allow some normal test on the array's contents also to function as a termination test. For example, a highly optimized routine for finding a value in an array might artificially place a copy of the value to be searched for after the last slot of the array, thus allowing the main search loop to search for the value without having to check at each pass whether the end of the array had been reached. 3. [among users of optimizing compilers] Any technique, usually exploiting knowledge about the compiler, that blocks certain optimizations. Used when explicit mechanisms are not available or are overkill. Typically a hack: "I call a dummy procedure there to force a flush of the optimizer's register-coloring info" can be expressed by the shorter "That's a fence procedure".

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fencepost error n.

1. [common] A problem with the discrete equivalent of a boundary condition, often exhibited in programs by iterative loops. From the following problem: "If you build a fence 100 feet long with posts 10 feet apart, how many posts do you need?" (Either 9 or 11 is a better answer than the obvious 10.) For example, suppose you have a long list or array of items, and want to process items m through n; how many items are there? The obvious answer is n - m, but that is off by one; the right answer is n - m + 1. A program that used the `obvious' formula would have a fencepost error in it. See also [5044]zeroth and [5045]off-by-one error, and note that not all off-by-one errors are fencepost errors. The game of Musical Chairs involves a catastrophic off-by-one error where N people try to sit in N - 1 chairs, but it's not a fencepost error. Fencepost errors come from counting things rather than the spaces between them, or vice versa, or by neglecting to consider whether one should count one or both ends of a row. 2. [rare] An error induced by unexpected regularities in input values, which can (for instance) completely thwart a theoretically efficient binary tree or hash table implementation. (The error here involves the difference between