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Ben Halpern
Ben Halpern Subscriber

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Share a code snippet in any programming language and describe what's going on

#discuss #watercooler

Top comments (64)

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ben profile image
Ben Halpern •

I'll go first with Ruby

class String
  def like_a_cow
   "Moo #{self} mooooo"
  end
end

"Hello".like_a_cow
=> "Moo Hello mooooo"
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Classes in Ruby can be easily modified. The above code adds the like_a_cow method to String... So now the whole program can make a string "moo", like above.

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maxart2501 profile image
Massimo Artizzu •

In JavaScript it's:

String.prototype.like_a_cow = function() {
  return `Moo ${this} mooooo`;
};
"Hello".like_a_cow()
> "Moo Hello mooooo"
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I wonder how many languages allow this?

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ryencode profile image
Ryan Brown • • Edited

C# allows this,


    public static class StringExtension
    {
        public static string LikeACow(this string self)
        {
            return $"Moo {self} mooooo";
        }
    }
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you can now use this as

Console.WriteLine("Hello".LikeACow());
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I use extensions a lot on sealed library classes to add Quality Of Life things. One example is creating cleaner methods for adding parameters to SQLClient ClientCommand objects as one liners instead of multi-command monstrosities. (ok, they aren't that big, but do look unclean)

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lionelrowe profile image
lionel-rowe •

I think it's different (safer) in C# though, right? Like you need to add using <namespace> for the new methods to be accessible. So it's not true monkey patching, which is generally dangerous and best avoided.

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ryencode profile image
Ryan Brown •

Indeed you would need to use the containing namespace. And are likely safer as it would be pretty hard to modify the behaviour of code outside of your intended changes. (I think you would have to try very hard to have any affect outside of your explicit calls to the extension methods)

I won't claim to know much about TRUE monkey patching, but wikipedia's Extension Methods and Monkey Patching articles do reference each other in suggestive ways. ;)

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arjunsahlot profile image
Arjun •

Python:

class str(str):
    def like_a_cow(self):
        return f"Moo {self} mooooo"

str("Hello").like_a_cow()
> "Moo Hello mooooo"
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I should add that this is not good practice. str is a built in function and you should not override it.

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kenbellows profile image
Ken Bellows •

I'll do you one better: if you define a dynamic getter using Object.defineProperty, you can make it look exactly like the Ruby example:

Object.defineProperty(String.prototype, 'likeACow', {
    get() {
        return `Moo ${this} mooooo`
    }
})

'Hello'.likeACow
> 'Moo Hello mooooo'
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jmfayard profile image
Jean-Michel 🕵🏻‍♂️ Fayard • • Edited 
fun String.likeACow() = "Moo $this mooo"
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Same thing in Kotlin, super handy.

EDIT: A big advantage with for example the JavaScript version monkey-patching String.prototype, is that the String class is not modified everywhere in your codebase.

It works like a normal function, you import the new function only if and where you need it. See kotlinlang.org/docs/extensions.htm...

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silverhairs profile image
Boris Kayi • • Edited

In Dart it's

extension on String{
 String get like_a_cow => 'Moo $this mooooo';
}

"Hello".like_a_cow;
=> "Moo Hello mooooo"
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leopfeiffer profile image
Leo Pfeiffer •

Similar in Scala:

extension(str: String) {
  def like_a_cow = s"Moo ${str} mooooo"
}

scala> "Hello".like_a_cow
val res0: String = Moo Hello mooooo
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maowtm profile image
maowtm •

In Rust you can add functions to other types with traits. This actually adds the like_a_cow function for all types that are printable, including strings. You have to use the trait though.

pub trait LikeACow {
    fn like_a_cow(&self) -> String;
}

impl<T: std::fmt::Display> LikeACow for T {
    fn like_a_cow(&self) -> String {
        format!("Moo {} mooooo", &self)
    }
}

fn main() {
    // need to `use LikeACow;` if used in other modules, but not here.
    let s = "hello";
    println!("{}", s.like_a_cow());
}
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darkwiiplayer profile image
𒎏Wii 🏳️‍⚧️ •

Nice example, but I think it could be refined somewhat

using (Module.new do
  refine String do
    def like_a_duck
      "#{self} quack quack"
    end
  end
end)

puts "Hello".like_a_duck
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sanzstez profile image
Alexandr Stets •

It is bad practice to do such things. Better use

module Extensions
  refine String do
    def like_a_cow
    end
  end
end
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and add in you class

use Extensions
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auroratide profile image
Timothy Foster •

Some regex I wrote in 2018:

/^(?:\*|\d\.)\s(.*)\r?\n([ \t]+(?:\*|\d\.)\s(?:.|\r?\n[ \t]+(?:\*|\d\.))*)/
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I've stared at it for 5 minutes and still can't tell you what's happening 🙃

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chrisgreening profile image
Chris Greening •

Dear programmer: When I wrote this code, only god and I knew how it worked. Now only god knows it! Therefore, if you are trying to optimize this routine and it fails (most surely), please increase this counter as a warning for the next person: total hours wasted here= 254

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tracygjg profile image
Tracy Gilmore •

If you throw the expression into something like Debuggex it can map out the routes through the expression, as follows.

RegExp diagram

However, whilst this shows what is happening it does not indicate why.

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auroratide profile image
Timothy Foster •

Now that I'm staring at this chart, I'm recalling that at some point I was trying to parse markdown. Pretty sure this is looking for nested lists:

* Hello!
  1. A nested ordered list
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Though, it is interesting to me that the initial * or \d\. is not captured; one would think it'd be important to distinguish between an unordered and ordered list...

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tracygjg profile image
Tracy Gilmore •

I studied the screenshot I attached to my comment and came to the same conclusion but it looks to me the expression might be more complicated than it needs to be - without fully understanding the context of course.

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bbrtj profile image
bbrtj •

It searches for indented sublists, like:

1. abc
  * def
  * ghi
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You're welcome.

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jamesthomson profile image
James Thomson •

Anyone that can read this and know exactly what's going on is clearly not human

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3kiruthick profile image
3Kiruthick •

Which purpose u wrote this regex

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lionelrowe profile image
lionel-rowe •

PHP

function lets_do_some_math($n) {
    return ($n / 2) / ($n / 2);
}

$a = lets_do_some_math(10);
$b = lets_do_some_math(11);

printf('%d %d %s', $a, $b, $a === $b ? 'yes' : 'no');
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Prints 1 1 no.

In PHP, the division operator / returns an integer if the two operands are both integers and divide exactly, and a float in all other cases. (10 / 2) thus gives int(5), while (11 / 2) gives float(5.5). Then, in the next division step, 5 / 5 gives int(1), while 5.5 / 5.5 gives float(1).

PHP's language design is truly astounding.

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rajarshi profile image
Rajarshi Bandopadhyay • • Edited

All right, let's see if you guys have a clue about this:

docker commit `docker ps -a |\
    head -n2 |\
    tail -n1 |\
    cut -d" " -f1` $1:$2
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This is a single line of shellscript code written over three lines for readability. Notice that it employs backticks inside the code.

A lot is happening here, obviously. FIrst of all, the $1 and $2 will be replaced by the first and second command line argument respectively. So if you are invoking this script with the command line arguments repo and tag, this will translate to:

docker commit `docker ps -a |\
    head -n2 |\
    tail -n1 |\
    cut -d" " -f1` repo:tag
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Next, note the backticks inside the command. The portion between the backticks - will first be evaluated. The result of this evaluation will then replace the entire thing inside the backticks.

Now, what does the portion inside the backtick do? Well, it has four parts:

Part 1 is docker ps -a, which yields a list of Docker images and their details:

CONTAINER ID   IMAGE          COMMAND                  CREATED         STATUS                     PORTS     NAMES
20d03205fe06   ubuntu:20.04   "bash"                   3 seconds ago   Exited (0) 2 seconds ago             bold_feynman
dcf460b2c4ff   07cd54330caf   "/bin/sh -c 'tar xzf…"   4 minutes ago   Up 4 minutes                         blissful_liskov
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This output is then piped into part 2. Piping is a special construct in Shellscript, which takes the string output of one command and puts it into the string input of the next command. So if command-1 prints 2+2+2 into the output, and command-2 evaluates mathematical expressions from keyboard and prints the output, then command-1 | command-2 will basically make the 2+2+2 from the first command become the input of the second, and we will only see the final output - 6.

The output of the first command is being piped into the second command, which is head -n2. The head command snipes out the first n lines from a file (or text input), and prints it. When fed the lines of details of different classes at the input, the head command will print the first n lines and then ignore the rest. We specify n with the -n2 flag, and its value is set to 2.

So the head command will print the first two lines from the table:

CONTAINER ID   IMAGE          COMMAND                  CREATED         STATUS                     PORTS     NAMES
20d03205fe06   ubuntu:20.04   "bash"                   3 seconds ago   Exited (0) 2 seconds ago             bold_feynman
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Notice that this includes the heading row and the details of the latest image - in this case, one which was created just three seconds before this command was run (I admit to having created it just to demonstrate this snippet).

The next command in the pipe is tail, and this command will ignore all but the last n lines from the input, and print those last n lines. In this case, we invoke it with tail -n1, thereby setting n to 1. The last one line will be printed.

20d03205fe06   ubuntu:20.04   "bash"                   3 seconds ago   Exited (0) 2 seconds ago             bold_feynman
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Or at least, tail will try to print it. But its own printed output has been further piped into the cut command. This command does something quite whacky: it takes two arguments, known as the delimiter and the selected columns. The delimiter has to be a char and the selected columns is a comma-separated sequence of numbers. In case a single number is provided, that single number is interpreted as a single-length sequence of numbers.

What cut does is that it splits each line of its input into parts, separated by the delimiter. It then takes the specific values which correspond to the selected columns, and then prints only those values which have been selected.

For instance, in this case, it will split the input string (which is a single line) by the " " space character, and then take out the first member of the resulting array of substrings. Of course, this effectively means that it will only pick the first word of the line. And in this case, that word is the container ID of the most recently run container:

20d03205fe06
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This ID is the final output of the entire portion inside the backticks, and given the way Shellscript works, the entire portion inside backticks will simply be replaced by this one container ID number:

docker commit 20d03205fe06 repo:tag
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Which is the final form of the command, and it is executed. So the command does this:

It commits the most recently run container as an image with the name and tag provided as command line arguments to the script

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pandademic profile image
Pandademic •

Wow.... That's actually quite useful

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rajarshi profile image
Rajarshi Bandopadhyay •

Thank you. I use this one a lot, though I typically write it out in just one line.

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dhravya profile image
Dhravya •

Here's a Rust moment, I tweeted it today lol

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jroes profile image
Jon Roes •

Is your text editor or some plugin showing the return types of the functions in the chain? That's pretty cool. What's the plugin/editor?

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dhravya profile image
Dhravya •

I'm using VScode with rust-analyzer extension

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sm0ke profile image
Sm0ke • • Edited

Nothing in c++

int main() { return 0; }
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tunaxor profile image
Angel Daniel Munoz Gonzalez • • Edited

This is an F# script that posts a Post like object to the json placeholder API and deserializes the json response to a Post.

you can copy into a file and run it like this:

  • dotnet fsi ./filename.fsx 
#r "nuget: FsHttp" // specify the http library

// open the required namespaces
open FsHttp
open FsHttp.DslCE
open System.Text.Json

// define the shape of the data
// these are known as Records in F#
type Post =
    { userId: int
      id: int
      title: string
      body: string }

// In F# records can't have null values for most types
// so we use an anonymous record (`{| |}` instead of `{}`)
// because we don't have an id value yet
let payload =
    JsonSerializer.Serialize(
        {| userId = 1
           title = "Sample"
           body = "Content" |}
    )

let response =
    // declare the request
    http {
        POST "https://jsonplaceholder.typicode.com/posts"
        body
        json payload
    }
    // send the request, it can also be done asynchronously
    |> Request.send
    // get the stream back (rather than downloading the response in bytes/string
    |> Response.toStream
    // deserialize it using .NET base class library classes like JsonSerializer
    |> JsonSerializer.Deserialize<Post>

// you can now check the response in the console
printfn "%A" response
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darkwiiplayer profile image
𒎏Wii 🏳️‍⚧️ • 
private["_min", "_max", "_mid", "_target", "_kit"];
_target = random(_sum);
_min = 0; _max = count _array -1;

while { _min != _max-1 } do {
   _mid = floor (_min + (_max - _min) / 2);
   if ( (_array select _mid select 0) <= _target )
      then { _min = _mid }
      else { _max = _mid };
};
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Does a binary search through an array and finds the first element with a value greater than a random target at index 0.

This is a part of a script that chooses a random set of items to put in a supply box where each item set can have a weight assigned to it based on how valuable the items are (higher weight means more common)

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pandademic profile image
Pandademic •

what language is that?

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darkwiiplayer profile image
𒎏Wii 🏳️‍⚧️ •

SQF :D

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yassineldeeb profile image
Yassin Eldeeb 🦀 •

I'm gonna bet on Brainf*ck, so here's mine.

>+++++[>+++++++<-]>.<<++[>+++++[>+++++++<-]<-]>>.+++++.<++[>-----<-]>-.<++
[>++++<-]>+.<++[>++++<-]>+.[>+>+>+<<<-]>>>[<<<+>>>-]<<<<<++[>+++[>---<-]<-
]>>+.+.<+++++++[>----------<-]>+.<++++[>+++++++<-]>.>.-------.-----.<<++[>
>+++++<<-]>>.+.----------------.<<++[>-------<-]>.>++++.<<++[>++++++++<-]>
.<++++++++++[>>>-----------<<<-]>>>+++.<-----.+++++.-------.<<++[>>+++++++
+<<-]>>+.<<+++[>----------<-]>.<++[>>--------<<-]>>-.------.<<++[>++++++++
<-]>+++.---....>++.<----.--.<++[>>+++++++++<<-]>>+.<<++[>+++++++++<-]>+.<+
+[>>-------<<-]>>-.<--.>>.<<<+++[>>++++<<-]>>.<<+++[>>----<<-]>>.++++++++.
+++++.<<++[>---------<-]>-.+.>>.<<<++[>>+++++++<<-]>>-.>.>>>[-]>>[-]<+[<<[
-],[>>>>>>>>>>>>>+>+<<<<<<<<<<<<<<-]>>>>>>>>>>>>>>[<<<<<<<<<<<<<<+>>>>>>>>
>>>>>>-]<<+>[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-[-
[-[-[-[-[-[-[-[-[-[-[-[<->[-]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]<[
<<<<<<<<<<<<[-]>>>>>>>>>>>>[-]]<<<<<<<<<<<<[<+++++[>---------<-]>++[>]>>[>
+++++[>+++++++++<-]>--..-.<+++++++[>++++++++++<-]>.<+++++++++++[>-----<-]>
++.<<<<<<.>>>>>>[-]<]<<<[-[>]>>[>++++++[>+++[>++++++<-]<-]>>++++++.-------
------.----.+++.<++++++[>----------<-]>.++++++++.----.<++++[>+++++++++++++
++++<-]>.<++++[>-----------------<-]>.+++++.--------.<++[>+++++++++<-]>.[-
]<<<<<<<.>>>>>]<<<[-[>]>>[>+++++[>+++++++++<-]>..---.<+++++++[>++++++++++<
-]>.<+++++++++++[>-----<-]>++.<<<<<<.>>>>>>[-]<]<<<[-[>]>>[>+++[>++++[>+++
+++++++<-]<-]>>-.-----.---------.<++[>++++++<-]>-.<+++[>-----<-]>.<++++++[
>----------<-]>-.<+++[>+++<-]>.-----.<++++[>+++++++++++++++++<-]>.<++++[>-
----------------<-]>.+++++.--------.<++[>+++++++++<-]>.[-]<<<<<<<.>>>>>]<<
<[<+++[>-----<-]>+[>]>>[>+++++[>+++++++++<-]>..<+++++++[>++++++++++<-]>---
.<+++++[>----------<-]>---.<<<<<<.>>>>>>[-]<]<<<[--[>]>>[>+++++[>+++++++++
<-]>--..<+++++++[>++++++++++<-]>-.<+++++[>----------<-]>---.[-]<<<<<<.>>>>
>]<<<[<+++[>----------<-]>+[>]>>[>+++[>++++[>++++++++++<-]<-]>>-.<+++[>---
--<-]>.+.+++.-------.<++++++[>----------<-]>-.++.<+++++++[>++++++++++<-]>.
<+++++++[>----------<-]>-.<++++++++[>++++++++++<-]>++.[-]<<<<<<<.>>>>>]<<<
[--[>]>>[>+++++[>+++++[>+++++<-]<-]>>.[-]<<<<<<<.>>>>>]<<<[<++++++++++[>--
--------------<-]>--[>]>>[<<<<[-]]]]]]]]]]]>>]<++[>+++++[>++++++++++<-]<-]
>>+.<+++[>++++++<-]>+.<+++[>-----<-]>.+++++++++++.<+++++++[>----------<-]>
------.++++++++.-------.<+++[>++++++<-]>.<++++++[>+++++++++++<-]>.<+++++++
+++
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Please don't ask what it does, cause I've no idea, it just looks cool..I guess.

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ashleyjsheridan profile image
Ashley Sheridan • • Edited 
10 PRINT "You been hacked!"
20 GOTO 10
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BASIC hacking

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ben profile image
Ben Halpern •

whoa

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