在你看来，你遇到过的最令人惊讶、最怪异、最奇怪或最“WTF”的语言特性是什么?
请每个回答只回答一个特征。
当前回答
我一直想知道这个函数在Java Core库的Math类中的用途:
static double expm1(double x); // Returns e^x - 1.
其他回答
COMEFROM是我见过的最奇怪，也可能是最没用的语言功能。
其次是三元运算符，因为它违反了优化的第一条规则。它带来的危害大于它解决的问题。它的危害更大，因为它使代码可读性更差。
并不是一个真正的语言功能，但有趣/很棒的功能使用是Duff的设备。
在Java中可以抛出任何可抛出的东西。
class YourBoss extends Throwable {
}
public class Main{
public void main(String[] s) throws YourBoss {
try{
throw new YourBoss();
}catch(Exception e){
}catch(Error e){
}
}
}
在Perl中，可以通过修改一个类的@ISA数组来改变它的继承链，这让我很惊讶。
package Employee;
our @ISA = qw(Person);
# somwhere far far away in a package long ago
@Employee::ISA = qw(Shape);
# Now all Employee objects no longer inherit from 'Person' but from 'Shape'
Haskell's use of Maybe and Just. Maybe a is a type constructor that returns a type of Just a, but Maybe Int won't accept just an Int, it requires it to be a Just Int or Nothing. So in essence in haskell parlance Just Int is about as much of an Int as an apple is an orange. The only connection is that Just 5 returns a type of Maybe Interger, which can be constructed with the function Just and an Integer argument. This makes sense but is about as hard to explain as it can theoretically be, which is the purpose of haskell right? So is Just really JustKindaLikeButNotAtAll yea sorta, and is Maybe really a KindaLooksLikeOrIsNothing, yea sorta again.
-- Create a function that returns a Maybe Int, and return a 5, which know is definitly Int'able
> let x :: Maybe Int; x = 5;
<interactive>:1:24:
No instance for (Num (Maybe Int))
arising from the literal `5' at <interactive>:1:24
Possible fix: add an instance declaration for (Num (Maybe Int))
In the expression: 5
In the definition of `x': x = 5
> Just 5
Just 5
it :: Maybe Integer
-- Create a function x which takes an Int
> let x :: Int -> Int; x _ = 0;
x :: Int -> Int
-- Try to give it a Just Int
> x $ Just 5
<interactive>:1:4:
Couldn't match expected type `Int' against inferred type `Maybe t'
In the second argument of `($)', namely `Just 5'
In the expression: x $ Just 5
In the definition of `it': it = x $ Just 5
祝你好运读到这篇文章，我希望它是正确的。
让我们为所有试图废除保留词的语言(如PL/I)投票。
还有什么地方可以合法地写出这样有趣的表达:
IF IF THEN THEN = ELSE ELSE ELSE = THEN
(IF, THEN, ELSE是变量名)
or
IF IF THEN THEN ELSE ELSE
(IF为变量，THEN和ELSE为子程序)
