Write a function that shows off something unique or interesting about the language you're using

Comments

[Pierre Bouillon]

Unique and interesting, but awful

Python 2.X:

>>> True
True
>>> True = False
>>> True
False

Python is full of very tricky things ! I had a lot of fun reading this README which explains them.

[Alexandr K]

never know it. it looks like js nightmare. :)

[rhymes]

Fortunately it's gone in Python 3:

>>> True
True
>>> True = False
  File "<stdin>", line 1
SyntaxError: can't assign to keyword

:D

[Pierre Bouillon]

It's no longer an integer :)

[Valentin Baca]

It still is. bool is a subclass of int:

$ python3
Python 3.6.5 (default, Mar 30 2018, 06:42:10)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> isinstance(True, int)
True
>>> isinstance(False, int)
True

[Pierre Bouillon]

Shameful mistake, thanks for clarifying ! I meant that they had their own type now, indeed from integer.

Full explanation

Initially, Python used to have no bool type 
(people used 0 for false and non-zero value like 1 for true). 
Then they added True, False, and a bool type, but, for backward
compatibility, they couldn't make True and False constants- they 
just were built-in variables.

[Tamás Szelei]

That readme is excellent, thanks for posting it!

[sreenivas]

Ah!!! Looks like Python is a distant relative of Javascript!!

[Ben Halpern]

In Ruby we can monkeypatch to easily add functionality to any class.

For example:

class String

  def yell!
    self.upcase + "!!!"
  end

end

I'm extending the string class so that "hello".yell! outputs "HELLO!!!"

And now all strings in the program have access to the yell! method. ❤️

I'll add that this is sort of bonkers and an easy way to add some really hard-to-debug code to an app. Use with great fear and caution.

[Sung M. Kim]

That's amazing that Ruby and other languages can extend built-in classes as well.

Anyways, to show off C#, here you go.

C# can extend any classes using extension method syntax.

using System;

namespace extensionmethod
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!".Yell());
        }
    }

    public static class StringExtensions
    {
        public static string Yell(this string message)
        {
            return $"{message.ToUpper()}!!!";
        }
    }
}

Outputs

c:\misc\Sources\throwaway\extensionmethod>
$ dotnet run
HELLO WORLD!!!!

Note that you should mark the parameter with this

Yell(this string message)...

[Christian Vasquez]

Here's how this would look in Kotlin:

fun String.yell() = this.toUpperCase()

Another interesting use is to create an Extension Property so you can print any type to the console, like this:

// Define the extension property
val Any.sout
    get() = println(this)

Which can be used like:

fun main(args: Array<String>) {
    "hi".sout // prints hi
    123.sout  // prints 123
    true.sout // prints true
}

Since this is also available on any other class, any object you create will also have this property and it will call their toString().

[Kasey Speakman]

In F# it is also easy to add functionality to existing classes.

type String with

    member me.yell () =
        me.ToUpper() + "!!!"

You can also add functions to existing static classes (modules) too.

module Array =
    let shuffle arr =
        ...

[| for i in 0 .. 23 do yield i * i |]
    |> Array.filter isOdd   // filter is built-in
    |> Array.shuffle        // i added

[Dave Cridland]

Lots of languages support that, including most obviously Javascript.

[Alain Van Hout]

Interesting. Is that possible via class definitions (class syntax I mean) or only via the prototype syntax?

[Sung M. Kim]

A PowerShell script to get 5 most CPU intensive processes.

PowerShell passes .NET CLI object(s) into the next pipeline (<-- this is most unique feature of all shells) so there is need to parse text as you do in other shells (using sed or awk).

PS C:\misc\sources> gps | sort -desc cpu | select -first 5 id, cpu, processname

   Id         CPU ProcessName
   --         --- -----------
 9352 7230.578125 firefox
13124 6531.015625 firefox
10460      6419.5 firefox
 2296  6017.03125 firefox
 9172 4406.453125 firefox

[Vinay Pai]

This is pretty neat

[Sung M. Kim]

Thanks Vinay.

[edA‑qa mort‑ora‑y]

Leaf stores literals (constants) as rational numbers and is type safe.

good is assigned the value 1 -- there is no precision loss on the division.

err produces a compiler error since 1/3*2 is not an integer.

[W. Brian Gourlie]

Woah. How do rational numbers interact with irrational numbers in this case? Are they approximated prior to any sort of arithmetic or are they considered incompatible types?

[edA‑qa mort‑ora‑y]

π and 1/2 were my two motivating reasons for making this feature.

For irrationals, and other fractions, the system will switch to a high-precision floating point mode instead of a rational -- I honestly don't remember what the trigger criteria actually is, I think size of the rational.

What this allows however is that π is a single constant you can define to 100 decimal places. This is high enough precision that several constant operations, basic math, can work on this value without losing precision when converting to the actual system type. It doesn't matter if you convert to a 32/64/128-bit float, it'll have the full precision for that type. No need for constants per type, or stuff like M_PI2.

Note this precision only applies to constants. Runtime variables are limited by the standard system types. Sometime later I'll add these numbers are runtime, but they're fairly special purpose at that point. The literal folding now is enough to cover the current intended use-cases.

[Christian Vasquez]

Kotlin has this concept of infix functions, which means they are an extension function that has only 1 parameter and allows us to use them without the dot (.) operator and no parentheses (but you can also do it the normal way, if you want to).

Declare the infix function

infix fun Int.times(base: Int) = this * base

Example

fun main(args: Array<String>) {
    println(10 times 5)  // prints 50
    println(10.times(5)) // also prints 50
}

[Sung M. Kim]

JavaScript lets you swap variables without a temporary variable.

$ node
> let a = 1, b = 999
undefined
> [b, a] = [a, b]
[ 1, 999 ]
> a
999
> b
1

[Dave Cridland]

So does C:

int a = 1, b = 999;
a ^= b;
b ^= a;
a ^= b;

OK, so this is specific to numeric values, actually, but it comes in handy in cryptographic code for constant time conditional swaps and things.

[Sung M. Kim]

Thanks Dave.
There is no end to learning.
I feel humbled :)

[rhymes]

Same in Python

>>> [a, b] = [1, 999]
>>> a, b
(1, 999)
>>> [b, a] = [a, b]
>>> a, b
(999, 1)

[Sung M. Kim]

Python has been on my mind lately. That's yet another good reason ;p

[Dave Cridland]

Javascript... Yes, Javascript is a barrel of pure quirk. Just pick variable scope. As if it wasn't bad enough that hoisting exists, the bizarre way scopes work allows you to write some truly awe-inspiring hackery, like this Fibonacci function:

function fib(n) {
  if (n) {
    a = 1;
    b = 0;
    c = n + 1;
  }
  if (c === 1) {
    return a + b;
  }
  c = c - 1;
  let d = a + b;
  b = a;
  a = d;
  return fib();
}

[Ross Henderson]

It isn't that difficult to generate the Fibonacci Spiral through Oracle SQL :)

with FIBONACCI (i, FIBO, PREV) as 
(
   select 
      1 i,
      0 FIBO,
      cast( null as number ) PREV 
   from 
      DUAL
   union all
   select 
      f1.i + 1  i,
      f1.FIBO + nvl(f1.PREV,1) FIBO,
      f1.FIBO PREV
   from 
      FIBONACCI f1
   where 
      f1.i < 20
)

select 
   FIBO
from 
   FIBONACCI
order by 
   i;

[Dave Cridland]

Right - something like this is fine:

class Foo {
  method1() {
    console.log("Method one")
  }
}

Foo.prototype.method2 = function(){ console.log("Method too") }

Thanks to the batshit insane way that this works, it's a full-blown method.

This capability isn't unusual. In Python, you can also add methods to instances, but you need to ensure you handle self:

class Foo:
  def __init__(self):
    # Some code

f = Foo()

dir(f) ## Returns ['__doc__', '__init__', '__module__']

Foo.method = lambda self, x: x

dir(f) ## Now includes our new method

f.method(22) ## Returns 22.

Languages such as C++ and Java, on the other hand, have immutable types (and in the former, types aren't themselves even a type).

[Saurabh Sharma]

1 == '1' // true
1 === '1' //false 

JavaScript