Strangest Language Features

http://stackoverflow.com/questions/1995113/strangest-language-feature

by antoviaque • 15 years ago

129 73 15 years ago

xd• 15 years ago

PHP; converts array('123' => 0); into array(123 => 0);

Which I came across as a problem when working with mongodb as it will only except strings as keys (not sure if this is enforced by PHP and/or mongo). Luckily you can create a class with numeric properties and pass that to mongodb which will then be treated as strings i.e

$array = new stdClass; $array->{123} = 0;

derleth• 15 years ago

> only except strings

A strange feature of the English language is that this doesn't work; you have to use 'accept' here.

darklajid• 15 years ago

Second SO repost. Previously discussed with > 80 comments here:

https://news.ycombinator.com/item?id=1601062

danso2• 15 years ago

I have to admit that I upvoted the post because I had never seen this before, and the previous discussion is nearly 1.5 years old.

That said....how did this get resubmitted? They both have the exact same URL

---- # edit: I see...one URL is http://stackoverflow.com/questions/1995113/

The other has a slug in it: http://stackoverflow.com/questions/1995113/strangest-languag...

I thought HN had some kind of redirect-autofollow that sniffed this kind of thing out? Or at least that's why I assumed hitting "submit" can result in a long delay, even before you're told that the title is > 80 (I wish there were a javascript validator for title length, while I'm pondering things...)

chc4• 15 years ago

Nope, even just appending a slash to a URL will get you past the dupe filter. Even beyond that, though, the filter only looks at recently accessed posts, so something with that long a gap between reposts almost certainly wouldn't get flagged.

danso2• 15 years ago

Wow...not a single SO response that said Ruby? I guess that's a good thing for us Rubyists?

cobrausn• 15 years ago

Actually, there is, just not as many upvotes as the others.

http://stackoverflow.com/a/2026849

Basically, it is possible to inherit a random class in ruby.

    class RandomSubclass < [Array, Hash, String, Fixnum, Float, TrueClass].sample
       ...
    end

raganwald2• 15 years ago

I wouldn’t call that a strange feature, just a surprising consequence of an un-strange feature, namely that inheritance involves expressions and that classes are first-class entities.

Folks from certain other languages would be just as surprised to find out that you can alias classes by assigning them, return them from functions, and so on.

judofyr2• 15 years ago

Someone else is probably going to mention flip-flops, so let me show you "defined?":

    a = 1
    defined?(a) # => "local-variable"
    defined?(p) # => "method"
    defined?(nothing) # => nil

defined? is a syntax-construct (not a method) which tries to tell you if its "parameter" is defined. The rules for this are rather interesting.

    class String
      def print
        p self
        self
      end
    end

Okay, String#print is just a helper method to prove my point.

    defined?("hello".print)        # => "method"
    defined?("hello".print.strip)  # => prints out "hello", then returns "method"
    defined?("hello".print.stripp) # => prints out "hello", then returns nil

Okay, so defined? may actually call methods for you to figure out if it's "defined" or not. What if we try something more complex:

    defined?(if true then "hello".print.strip end) # => "expression"

Wait, what? This does not call the print method. In fact, this check is done entirely at parse-time. "defined?(if true then … end)" will always return "expression". In fact, anything more complex than local variables, method calls or constant names will just return "expression". Well, except for "defined?" though; defined? can't check itself - it's a syntax error.

Another intresting "feature": If any exception is raised, the whole expression is considered undefined:

    class String; def print; raise; end; end
    
    defined?("hello".print.strip) # => nil

judofyr2• 15 years ago

Another one: class variables!

    # Define two class variables in two different classes:
    class MyClass
      @@base = 1
    end
    
    class OtherClass
      @@base = 2
    end
    
    # Define it in the superclass too:
    class Object
      @@base = 3
    end

    class MyClass
      # Magic! The subclass-variable has now changed!
      p @@base # => 3
    end

    class OtherClass
      # In both classes in fact:
      p @@base # => 3
      
      # And finally, let's reset this:
      @@base = 4
    end

    class Object
      # Whoops, this changes the superclass too:
      p @@base # => 4
    end

Explanation: Two class variables with the same name can't exists in the same class hierachy. Therefore, class variable lookup (and setter) will always traverse to the upmost-class where the variable is defined.

(Hope you don't mind that I wrote these in two different posts.)

Dove• 15 years ago

I'm still reeling from finding out that zero is true.

atlbeer• 15 years ago

This is an evil bug in Javascript

parseInt('06') // 6

parseInt('07') // 7

parseInt('08') // 0

parseInt('09') // 0

parseInt('10') // 10

parseInt should really return NaN for '08', '09' etc

gcp4• 15 years ago

Octal notation, with an invalid number. Makes perfect sense.

It's not a bug, behaves like specified:

https://developer.mozilla.org/en/JavaScript/Reference/Global...

If parseInt encounters a character that is not a numeral in the specified radix, it ignores it and all succeeding characters and returns the integer value parsed up to that point. parseInt truncates numbers to integer values. Leading and trailing spaces are allowed.

[...]

For this reason always specify a radix when using parseInt.

chc4• 15 years ago

I really don't see how it makes perfect sense for a value which is not by any stretch of imagination a valid octal number to be interpreted as an octal number. Imagine if `parseInt('foo')` gave 38274 — would you also think that made perfect sense?

Also, that document says the behavior is nonstandard, so I don't even see how you can say it's behaving as specified.

groby_b2• 15 years ago

"Behaves as specified", "makes perfect sense", and "not a bug" are three entirely different concepts.

It does _not_ make perfect sense to anybody who's never used octal. That is presumably the vast majority of anybody born past, say, 1980.

As such, it _is_ a bug in the sense that it violates expectations. It's just a bug in the spec, not in the code.

barrkel• 15 years ago

Following a spec is not a valid excuse for it not being a bug. Specs have bugs too; sometimes they're even designed in, deliberately, to make companies not look bad, or to preserve backward compatibility.

For a parser to ignore trailing garbage after it has parsed as far as it can is usually a sign of a poor-quality parser. On topic: an odd feature of Pascal is that all text following the final 'end' '.' in the file is ignored. But good quality compilers still issue a warning.

Tangurena• 15 years ago

While JavaScript is parsing it as octal, this will cause a whole raft of errors if you are making your users enter dates.

User enters 08 for August, even returning NaN would be a mistake.

shadowfiend2• 15 years ago

You can and should then pass the second radix parameter to parseInt:

    parseInt('08', 10) // => 8

This tells it explicitly that this is a base-10 number, rather than letting it guess at the base. You can also use this to decode things in base n, n <= 36.

burgerbrain• 15 years ago

It is my impression that the PHP interpreter will, or at least used to, do this to you. Instead of you know, giving you an error like most languages do...

Much worse than this one obviously, caused if I recall by not checking how strtol set endptr.

niyazpk• 15 years ago

In JavaScript:

    (NaN === NaN) is false
    (NaN !== NaN) is true

raganwald2• 15 years ago

This is isomorphic to NULLs in some languages (I think SQL behaves this way). Basically, NaN isn’t some specific thing, it’s an indication of something that isn’t a number. So two things that aren’t numbers can’t be thought to be equal to each other, they might be radically different things.

If there’s a WTF, it’s that NaN === NaN is either true or false. If I were writing a language, it might be undecideable. But if you end up with:

    Undecideable === Undecideable //=> Undecideable

You are opening up the “Hopelessly Egocentric Null” can of worms:

https://github.com/raganwald/homoiconic/blob/master/2009-02-...

masklinn6• 15 years ago

> I think SQL behaves this way

Yes. It's also how NaNs are supposed to work according to IEEE-754.

The only reason why it can be strange in javascript is that it's pretty common to encounter nans in JS as the language tries very hard not to throw errors and likes nans a lot (so `parseInt('foo')` returns NaN instead of `null` or an error), whereas it's very rare in other languages. Pretty much all languages have nans, and all nans behave this way. Here it is in Python:

    >>> float('nan')
    nan
    >>> float('nan') == float('nan')
    False
    >>> float('nan') != float('nan')
    True
    >>> a = float('nan')
    >>> a == a
    False
    >>> import decimal
    >>> decimal.Decimal('NaN')
    Decimal('NaN')
    >>> decimal.Decimal('NaN') == decimal.Decimal('NaN')
    False
    >>> a = decimal.Decimal('NaN')
    >>> a == a
    False

edit: now that I think about it, there is a difference: in SQL, all operations involving `NULL` (including comparisons) return `NULL`, so `NULL = NULL` => `NULL` and `NULL != NULL` => `NULL`.

chc4• 15 years ago

That's not a JavaScript feature; it's part of the IEEE 754 standard for floating point numbers. NaNs are unordered. Every language that provides standard floating point numbers does it that way.

shadowfiend2• 15 years ago

Specifically, testing for NaN should be done using the isNaN function, never equality. That's not expounded on as often as necessary, I think heh.

rimantas• 15 years ago

This is correct and good. Whats funny, that typeof NaN is "number" :)

protomyth• 15 years ago

Icon's conditional statements were pretty odd http://en.wikipedia.org/wiki/Icon_(programming_language)

ww520• 15 years ago

The Multi-Dimensional Analog Literals template in C++ is amazing.

bitwize• 15 years ago

COBOL's ALTER statement.

As if COBOL weren't WTFy enough, the statement ALTER X TO PROCEED TO Y changes any subsequent GOTO X statement to go to Y instead. Meaning it's anybody's guess where a given GO TO, considered in isolation, goes to!

Someone2• 15 years ago

I upvoted you because it is the first thing I think of when I think of this question, but in Cobol's defense, self-modifying code (http://en.wikipedia.org/wiki/Self-modifying_code) was fairly normal at the time COBOL was conceived.

For a nice example from a later date, look at the GetChar subroutine on Commodore Basic. It loaded a byte from a hard-coded address, and then updated that address (hm, probably in the reverse order, since, IIRC, it shared code with GotChar, which returned the last value GetChar returned)

masklinn6• 15 years ago

Smalltalk's "cascading" operator is a strange (in the nicest way possible, it's mostly strange that nobody else has it) feature: a pretty popular style in OO languages these days is "fluent interfaces", in which methods return their `this` and — through method chaining — developers can call several methods on the same object while limiting verbosity. This style is of course possible in smalltalk:

    foo.bar().baz()

becomes

    foo bar baz

and if `bar` returns `self`/`this`, `baz` will be called on the same object. However, this has the issue that method implementors have to choose between fluent interfaces and returning useful values, as the fluency is decided by the return value domain for the method.

Smalltalk sidesteps this by having an operator `;` which essentially means "the message after this operator is sent to the same object as the message before this operator". As a result, in the example above you could have `bar` returning the height of the empire state building, and you'd still get the exact same result by writing:

    foo bar ; baz

(a message cascade returns the value returned by the last message)

Smalltalk was/is not fond of literal syntaxes, so its collection APIs (as far as adding to them goes anyway) look a lot like Java's, yet you could write things in a terser manner by using cascading:

    c := (ArrayList new) add: 3
                       ; add: 4
                       ; add: 5
                       ; add: 6
                       ; yourself.

is equivalent to:

    c := ArrayList new.
    c add: 3.
    c add: 4.
    c add: 5.
    c add: 6.

(note `yourself`, which does exactly what it says: it returns its `self`)

(and yes I know you can combine Java's anonymous subclasses and instance initializers to get something similar, in the specific case of instantiating non-final collections).

munificent• 15 years ago

> it's mostly strange that nobody else has it

For what it's worth, we're working on adding it to Dart. I don't think it's a done deal yet, but I believe we're close to having something finalized.

bokchoi• 15 years ago

> it's mostly strange that nobody else has it

It looks like it is the same as clojure's doto macro:

http://clojuredocs.org/clojure_core/clojure.core/doto

And it is strange more languages don't have it.

masklinn6• 15 years ago

It is pretty nice (and makes Clojure jump up a place or two in the completely unranked list of "languages I really need to learn"). It looks very similar yes, although there's a difference in that `doto` can only returns its `this`.

Someone2• 15 years ago

'with' (Pascal, MS Visual Basic, possibly others) is somewhat equivalent (it lacks the ability to return self) but more explicit:

  c := LeftAsAnExerciseForTheReader();
  with c do
  begin
    Add(3);
    Add(4);
    Add(5);
    Add(6);
  end;

grogs• 15 years ago

I've missed this feature in other languages.

Now I have a name, the cascades operator.

I don't think the syntax is especially elegant/readable, though.

gnaritas3• 15 years ago

It's extremely elegant and readable, when done idiomatically.

  list := OrderedCollection new
            add: 1;
            add: 2;
            add: 3;
            yourself

There's actually a literal syntax for Arrays, but the above example applies to all code and is used heavily in constructors and anything using a builder pattern.

spullara• 15 years ago

So, if you know Java has a similar syntax that is the same terseness, why mention it without example? I've found that many people don't know of it:

In Java this is:

List<Integer> c = new ArrayList<>() {{ add(3); add(4); add(5); add(6); }};

masklinn6• 15 years ago

> So, if you know Java has a similar syntax that is the same terseness, why mention it without example?

1. Because it's more limited in that it can only initialize an object and it requires that the type being initialized be non-final

2. Because it's kind-of a hack, using instance initializers (itself not a well-known feature) and anonymous classes (not overly common for concrete classes in java) simultanously

I also like to think people can be delighted in looking for treasures after a hint, and it's not too hard to find references to that trick, whereas references to Smalltalk's cascading operators are sparse and lost in the noise.

edanm• 15 years ago

I love the first answer to that question. And not just because I wrote it :)

A little bit of C trivia:

In C, arrays can be indexed like so:

a[10] which is very common.

However, the lesser known form (which really does work!) is:

10[a] which means the same as the above.

djcb• 15 years ago

similarly, the 'approaches' pseudo-operator:

while (i --> 0) { /* do something */ }

repsilat• 15 years ago

For some variety, there's also the left-handed "goes to" operator.

    while (5 <-- x) {} //omits the zero

and the much easier to type

    while (x --- 0) {} //equivalent to the "-->" operator

cjensen• 15 years ago

To be clear, it works because X[Y] is a synonym for * (X + Y)

Since addition is commutative, * (X + Y) can be rewritten as * (Y + X) which is a synonym for... Y[X]

kghose• 15 years ago

I have to say, this is what I come to HN for. I learned a lot from that link and doing wikipedia searches kept me entertained during lunch.

weinzierl• 15 years ago

Similar, but for more exotic languages: "What is the worst programming language you ever worked with?" http://stackoverflow.com/questions/961942/what-is-the-worst-...

nazar• 15 years ago

What about strangest programmers needs :D : http://stackoverflow.com/questions/8525199/how-to-store-java...

Edit: I think the title of the question was edited, the original was something like : "How to store javascript code in jquery variable without it executing?"

j_baker• 15 years ago

The fact that this question is closed is one of the things that annoys me the most about stackoverflow. It sometimes seems like people can't ask interesting questions without others getting offended.

philwelch• 15 years ago

Deletionists.

robryan• 15 years ago

Seems everything that isn't a direct question/answer gets closed. Seems like they miss an opportunity with the discussion questions. They have really smart community that can't really converse on the site of something doesn't fit into he narrow question and answer definition.

andrewflnr• 15 years ago

That's the whole point of StackOverflow. It's not a discussion platform. It's a Q&A platform. You can dispute whether that's a good idea, but they know exactly what they are doing.

Flimm• 15 years ago

Funnily enough, this is what I like most about stackoverflow. They know what they're good at, they know what use-cases the site is designed for, and they actively fight mission creep.

halo• 15 years ago

I find the amount of 'closed' questions on StackOverflow rather frustrating. I don't see how artificially restricting questions like this helps the site.

That said, I find the responses rather unsatisfying. Language design errors and quirks rather than unusual but useful features.

smackfu• 15 years ago

They just decided they didn't want to a polling site. I think the programmers stack exchange is where these questions go now, but who can tell? Generally I just post my questions somewhere obviously wrong and wait for someone to tell me where they go.

nandemo• 15 years ago

Counterpoint: I find it refreshing. In my opinion many otherwise interesting virtual communities degrade due to lack of some form of moderation.

I don't see it as artificially restricting questions. They're enforcing the rules that preserve the character and quality of the site. It's not arbitrary:

> This question is not a good fit to our Q&A format. We expect answers to generally involve facts, references, or specific expertise; this question will likely solicit opinion, debate, arguments, polling, or extended discussion.

There are other places for that sort of free-form discussion. Separating them from the factual Q&A is a win-win.

dustingetz• 15 years ago

i bet it does a woozey on their databases.

makmanalp• 15 years ago

No COME FROM?

http://en.wikipedia.org/wiki/COMEFROM http://c2.com/cgi/wiki?ComeFrom

icebraining• 15 years ago

It's in the middle of the first page: http://stackoverflow.com/a/1995275/221786

aerique• 15 years ago

Ah yes, all the Perl special variables! I actually did get scoffed at at work for using "use english" (while taking care it didn't affect regexps).

cousin_it• 15 years ago

For more JavaScript awesomeness on par with what's already presented, see http://wtfjs.com/ =)

tm123• 15 years ago

Identifiers with blanks:

http://tibleiz.net/zinc/

(not that strange, but not so common)

krzysz002• 15 years ago

Common Lisp has a global variable called read-base ,which controls also base numbers are read in with. This, IIRC, was put in because some earlier Lisps read numbers in octal, while others used decimal. Setting this variable to something higher than 10 can give you strange results. For example,

    nil
    => NIL
    (eql '() nil)
    => T
    (setf *read-base* 36)
    nil
    => 30477
    (eql '() nil)
    ERROR: 19101 is not a function name; try using a symbol instead
    (|EQL| '() nil)
    => NIL

For you non-lispers, the empty list '() is equal to the "false" value, nil. Also, the pipes are special syntax to allow for symbols which normally not parse as symbols. (The uppercase is for historical reasons too).

The moral of this story: "See that control variable over there, the one that does weird things to parsing? Don't touch it unless you know what you're doing."

RodgerTheGreat• 15 years ago

I presume that CL standardized on a base as a default, though? Otherwise you have an appropriately recursive problem that every base is "base-10" in that base.

edit: (setf read-base (+ 1 1 1 1 1 1 1 1 1 1)) :)

krzysz002• 15 years ago

I just went and checked, and the standard gives a default value of "10." for read-base , so decimal by default (I think). It also says:

"Notes:

Altering the input radix can be useful when reading data files in special formats. "

renownedmedia• 15 years ago

PHP: Personal favorite I used to quiz my students on:

$a = "5 Monkeys";

$b = "2 Bananas";

var_dump($a);

string(9) "5 Monkeys"

var_dump($a + $b);

int(7)

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