Today I learned

TIL about the simple_format method in Rails: https://api.rubyonrails.org/v8.0/classes/ActionView/Helpers/TextHelper.html

TIL about the four types of documentation

TIL about satisfy in RSpec. https://rspec.info/features/3-13/rspec-expectations/built-in-matchers/satisfy/

TIL that true and false don’t exist in standard C version:

gcc ./foo.c -o c && ./c
./foo.c:18:9: error: use of undeclared identifier 'true'
   18 |   while(true) {
      |         ^
1 error generated.

The values true and false can be imported by the stdbool library. Which declares them as integers:

// ...
#define true	1
#define false	0
// ...

Any non-zero value gets interpreted as True.

These are the small things that make me appreciate :ruby: and other high level languages.

Today (while debugging tag concatination) I learned that you can create mutable Strings in Ruby using +"foo" and immutable Strings using -"foo" https://docs.ruby-lang.org/en/4.0/String.html#method-i-2B

1. This one concatinates

label(...) + content_tag(...)

• This one returns just a mutable variant of the content tag:

label(...)
+ content_tag(...)

I expected + content_tag(...) to raise. Thanks for @Lukas Bischof

TIL that Rust doesn’t support traditional parameter overloading but you can still achieve it by implementing generic traits

This doesn’t compile:

impl Noise {
    pub fn new(seed: u32) -> Self {
        Self {
            seed,
            perlin: Perlin::new(seed),
        }
    }

    pub fn get(&self, position: DVec3) -> f64 {
        self.perlin.get(position.to_array())
    }

    pub fn get(&self, position: DVec2) -> f64 {
        self.perlin.get(position.to_array())
    }
}

This does:

pub trait NoiseSample<T> {
    fn get(&self, position: T) -> f64;
}

impl Noise {
    pub fn new(seed: u32) -> Self {
        Self {
            seed,
            perlin: Perlin::new(seed),
        }
    }
}

impl NoiseSample<DVec3> for Noise {
    fn get(&self, position: DVec3) -> f64 {
        self.perlin.get(position.to_array())
    }
}

impl NoiseSample<DVec2> for Noise {
    fn get(&self, position: DVec2) -> f64 {
        self.perlin.get(position.to_array())
    }
}

Would probably be less boilerplate if the library I am using here accepted structs instead of fixed length arrays.

TIL that fzf comes with vim plugin:

brew install fzf

vim.opt.runtimepath:append("/opt/homebrew/opt/fzf")

Open fuzzy search popup in NVIM with current dir:

:FZF

TIL that these two exist:

• https://charm-ruby.dev/
• https://www.ratatui-ruby.dev/

Today when implementing Quick-Sort in Ruby I learned about the block parameter shorthand _N. v is the 1st argument so it can be refactored as follows:

- l_part = a.filter { |v| v <= p }
+ l_part = a.filter { _1 <= p }

:vim: j0w→+

TIL about throwaway worktrees: git worktree add -d **<path>**** **which creates a new worktree with a detached HEAD at the same commit as the current branch

TIL that you can exit VIM using ZZ

TIL about repeated_permutation:

The “Old” Nested Way:

(0..31).each do |x|
  (0..31).each do |y|
    (0..31).each do |z|
      # Runs 32,768 times
      puts "Coordinate: #{x}, #{y}, #{z}"
    end
  end
end

The “New” DRY Way:

(0..31).to_a.repeated_permutation(3) do |x, y, z|
  # This automatically nests 3 levels deep
  # Runs 32^3 times
  puts "Coordinate: #{x}, #{y}, #{z}"
end

(Edit: formatting)

TIL about date.then in Ruby

my_object.date&.then { |d| I18n.l(d) }

As an alternative to:

I18n.l(my_object.date) if my_object.date.present?

Example:

my_object.date = nil
my_object.date&.then { |d| I18n.l(d) } || "-" # => "-"
my_object.date = 1.day.ago # => 2025-12-18 17:47:17.694132000 CET +01:00
my_object.date&.then { |d| I18n.l(d) } || "-" # => "Thu, 18 Dec 2025 17:47:17 +0100"

vs:

my_object.date = nil
my_object.date.present? ? I18n.l(my_object.date) : "-" # => "-"
my_object.date = 1.day.ago # => 2025-12-18 17:47:17.694132000 CET +01:00
my_object.date.present? ? I18n.l(my_object.date) : "-" # => "Thu, 18 Dec 2025 17:47:17 +0100"

color-mix! So I can change the transparency of my color defined in a CSS variable. https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/color_value/color-mix

background: color-mix(in srgb, var(--color-brown) 70%, transparent);

TIL that all requests in a controller go through a process method: https://github.com/rails/rails/blob/90a1eaa1b30ba1f2d524e197460e549c03cf5698/actionpack/lib/abstract_controller/base.rb#L145

 def process(action, ...)
      @_action_name = action.to_s

      unless action_name = _find_action_name(@_action_name)
        raise ActionNotFound.new("The action '#{action}' could not be found for #{self.class.name}", self, action)
      end

      @_response_body = nil

      process_action(action_name, ...)
 end

There is a nice test helper which @Alessandro Rodi made in 2017:

module InjectSession
  include Warden::Test::Helpers

  def inject_session(hash)
    Warden.on_next_request do |proxy|
      hash.each do |key, value|
        proxy.raw_session[key] = value
      end
    end
  end
end

TIL about the ActiveStorage Mirror Service: https://guides.rubyonrails.org/active_storage_overview.html#mirror-service to migrate assets like https://eidel.io/rails-how-to-migrate-s3-providers-via-activestorage-mirroring/

TIL that in VIM you can pass a buffer to a command and have it replace said buffer.

For example in a db/schema.rb file you could look for all table definitions as follows:

:%!rg 'create_table'

This passes the contents of the current buffer % to the command rg with the argument 'create_table' whose output is piped back to a buffer. So after entering that command you’d only have lines left containing create_table.

An additional utility I learned about in this context is tac

$ tac --help
Usage: tac [OPTION]... [FILE]...
Write each FILE to standard output, last line first.

With no FILE, or when FILE is -, read standard input.

This way you can reverse lines in your buffer using

:%!tac

current buffer %, ! indicates command, tac is the command being run on the contents of the buffer.

rails routes can be marked as internal: true and they will not be displayed by bin/rails routes. https://github.com/rails/rails/blob/af73d4ed24afa004cfacc628b17533c70bd7e056/railties/lib/rails/application/finisher.rb#L140

Today I found gold: https://github.com/rails/rails/blob/main/railties/lib/rails/commands/console/irb_console.rb

Here you can:

• alter the rails console prompt
• access ApplicationController instances and helpers
• create your new Rails app with app(true) in the Rails console
• alter the reload behaviour

TIL that if you want audible feedback for when your shell command has finished executing, you can just append “say”

rake export:generate_pdf && say "pdf generated"

https://github.com/silva96/log_bench can correlate requests

I can run robohash locally https://github.com/e1ven/Robohash

Bcrypt basically cuts the password after the 72nd character. This was discovered in a penetration test in one of our apps. https://github.com/heartcombo/devise/issues/5307

TIL about the Postgres OVERLAPS operator: https://www.postgresql.org/docs/current/functions-datetime.html#:~:text=In%20addition%20to%20these%20fun[…]20OVERLAPS%20operator%20is%20supported%3A

class Promotions::Tile < ApplicationRecord
  scope :overlapping, ->(range) {
    where("(starts_on, ends_on) OVERLAPS (?, ?)", range.begin, range.end)
  }
end

Promotions::Tile.overlapping(Date.today..Date.tomorrow)

Today I learned that Thoughtbot once tried to sell a CMS service called Copycopter: https://web.archive.org/web/20110719112035/https://copycopter.com/ It’s open sourced under https://github.com/copycopter/copycopter-server

I just had one of these moments again: “Oh, I never heard of this Rails feature, let’s look it up, it must be new.” Outcome: It’s there since ever: https://github.com/rails/rails/commit/889bf198577fd914e2814b9e402b49f972cf9551 It’s called ActionView::DependencyTracker and it tracks dependencies. This was done via regex and can be done with the Ruby parser since Rails 8.1.

SimpleCov was interfering with the coverage reports during subsequent task executions:

Having:

• 1 Spec that covers everything: → 100% line coverage

vs:

• 1 Spec that covers everything
• 1 Spec that skips a block → 70% coverage

The solution was to load the rails application tasks only once by changing the implementation

- before { Rails.application.load_tasks }
+ before(:all) { Rails.application.load_tasks }

Bonus:

- Rake::Task[task_name].reenable
- Rake::Task[task_name].invoke
+ Rake::Task[task_name].execute

I had a look at https://github.com/ankane/ahoy and learned about https://privacypatterns.org/ and the Anonymity Set, which can be used e.g. to identify a user without cookies. Applied here

You can save the commands entered in an iPython environment to a Python file using the %save magic method

In Switzerland, the correct spelling of time is 17.00, not 17:00. In contrast, Germany and Austria do use : as a separator.

TIL about CSS counter-increment property https://developer.mozilla.org/en-US/docs/Web/CSS/counter-increment

TIL about Python dictionary comprehensions:

nums = [0, 1, 2, 3, 4]
even_num_to_square = {x: x ** 2 for x in nums if x % 2 == 0}
print(even_num_to_square)

How to pass default values to variables in bash:

local base_latency="${1:-$BASE_LATENCY}"

takes the first argument or falls back to the variable BASE_LATENCY

TIL about tagged template literals in JavaScript https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals#tagged_templates

function sql(strings, ...values) {
  const query = strings.reduce((acc, str, i) => {
    return acc + str + (i < values.length ? "?" : "");
  }, "");
  return [query, values];
}

const userId = 42;
const status = "active";

const [query, params] = sql`SELECT * FROM users WHERE id = ${userId} AND status = ${status}`;

console.log(query);  // "SELECT * FROM users WHERE id = ? AND status = ?"
console.log(params); // [42, "active"] 

TIL that you should be careful with the spread syntax in Javascript. I encountered this when working on 1+ million numbers: https://stackoverflow.com/questions/1669190/find-the-min-max-element-of-an-array-in-javascript#comment45277115_1669222

There will be a Ruby Conference in Italy again next year

Where the name 37signals comes from: https://ui.adsabs.harvard.edu/abs/1993ApJ…415..218H/abstract

I can multiply a String with a Float:

"hello" * 3
=> "hellohellohello"

"hello" * 3.1
=> "hellohellohello"

"hello" * 3.5
=> "hellohellohello"

"hello" * 3.6
=> "hellohellohello"

"hello" * 4.0
=> "hellohellohellohello"

https://github.com/google/codesearch

TIL about formnovalidate https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/button#formnovalidate

TIL that responds_to?() only works for public methods UNLESS you provide the second optional parameter which has to be true

In German, there is a blank space before a “%”: 100 %, not 100%

TWL (Today We Learned) about the case in syntax in Ruby:

response = [201, { 'Content-Type' => 'application/json' }, '{"status":"ok"}']

case response
in [200..299, headers, body]
  puts "Success! Body: #{body}"
in [500, _, _]
  puts "Server Error!"
else
  puts "Unknown response"
end

# produces Success! Body: {"status":"ok"}

Today I learned that sqlite supports json data types.

TIL that you can “visit” a turbo frame:

Turbo.visit(url, { frame: "ctae_table" })

TIL that postgres enum values cannot be removed, only new ones can be added https://www.postgresql.org/docs/current/datatype-enum.html#DATATYPE-ENUM-IMPLEMENTATION-DETAILS

Add to your shell:

function mktouch() {
  mkdir -p -- "$(dirname -- "$1")" && touch -- "$1"
}

and then touch files with path (source: https://unix.stackexchange.com/a/688013/21833)

TIL about the unaccent PostgreSQL extension. Upon enabling it, you can remove accents using the unaccent function.

scope :by_last_name, ->(last_name) { where("unaccent(last_name) ILIKE unaccent(?)", "%#{last_name}%") }
scope :by_first_name, ->(first_name) { where("unaccent(first_name) ILIKE unaccent(?)", "%#{first_name}%") }

TIL that you can perform an empty match in Rust. This allows for pretty one-liners :)

let sprite_type = match () {
    _ if tile.is_flagged && !tile.is_revealed => TileSprite::Flag,
    _ if !tile.is_revealed => TileSprite::Uncovered,
    _ if tile.is_mine => TileSprite::Bomb,
    _ if tile.adjacent_mines > 0 => TileSprite::Number(tile.adjacent_mines),
    _ => TileSprite::Empty,
};

Today I learned about DISTINCT ON clause in Postgres. Very useful!

TIL about https://github.com/gogrow-dev/safe_polymorphic that allows to specify the polymorphic association types: belongs_to :owner, polymorphic: [Client, SubClient]

without the gem:

ALLOWED_OWNER_TYPES = %w(Client SubClient).freeze
validates :owner_type, presence: true, inclusion: { in: ALLOWED_OWNER_TYPES }

TIL about .presence, which is the same as Object.present ? Object : nil

TIL that params = { "a" => "a" } is NOT the same as params = { :a => "a" } and Ruby doesn’t understand it, when you try to access the String Key with a Symbol of the same name…

TIL that you can set table borders directly via html attributes: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/table#attributes

Example:

<table rules="rows">
  <thead>
    <tr>
      <th>Product</th>
      <th>Price</th>
      <th>Quantity</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Apples</td>
      <td>1.20</td>
      <td>10</td>
    </tr>
    <tr>
      <td>Bananas</td>
      <td>0.80</td>
      <td>5</td>
    </tr>
    <tr>
      <td>Oranges</td>
      <td>1.00</td>
      <td>8</td>
    </tr>
  </tbody>
</table>

So much easier to interpret .

TIL about the deprecated <font> tag.

<font color="blue" face="Arial, sans-serif">
  <h1>HTML maagic!</h1>
</font>

It is cool when you don’t feel like writing ANY css. More interesting html properties: https://html-only.netlify.app/#WHY

TIL that when I use a rich text column in Rails, I don’t need to actually have that column in the database :man-facepalming: It took me at least two hours of debugging and chatGPT helped me in 10 seconds.

tally method in ruby.

 %w[a b c b c a c b].tally # => {"a"=>2, "b"=>3, "c"=>3}

https://www.rubydoc.info/stdlib/core/Enumerable:tally

TIL that JavaFX Scene Builder can generate you a JRuby controller skeleton from your fxml layout:

class MainWindowController
    include JRubyFX::Controller

    # java_import 'com.gluonhq.charm.glisten.control.TextField'

    fxml 'MainWindow.fxml'

    # @labelTitle: 	Label
    # @textEntry: 	TextField
    # @textHistory: 	TextArea

    def addText(event) # event: ActionEvent

    end

    def clearTextEntry(event) # event: ActionEvent

    end
end

Today I learned two things at the same time.

• FactoryBot is very, very, very slow. Even attributes_for is not match to a hash.
• Usage of Turbo makes tests like this one quite involved

context "when there are many onboarding forms", :performance do
  before do
    city_and_date = "Winterthur, #{I18n.l(Date.today)}".freeze
    codes = 10_000.times.map { SecureRandom.alphanumeric(8) }.uniq
    attributes = codes.map.with_index do |code, index|
      {
        firstname: "Alex #{index}.",
        lastname: "Honnold",
        birthdate: "17.08.1985",
        accept_privacy: true,
        city_and_date: city_and_date,
        code: code,
        status: "draft"
      }
    end
    OnboardingForm.insert_all(attributes)

    sign_in user
  end

  it "loads in under 1 second" do
    time = Benchmark.measure do
      VCR.use_cassette("dato/onboarding_form") do
        get admin_onboarding_forms_path
      end

      expect(response).to have_http_status(:ok)
    end

    expect(time.real).to be < 1
    expect(response.body).to include("Max")
  end
end

TIL that the Java streams reduce method takes in two functions as arguments, allowing for parallel processing.

Example code:

List<String> words = Arrays.asList("hello", " ", "world", "!");

String combinedString = words.parallelStream().reduce("",
                                                     (currentString, nextWord) -> currentString + nextWord,
                                                     (s1, s2) -> s1 + s2);

System.out.println("Combined String: " + combinedString);

There’s a special breed of pig that looks like a sheep. https://en.wikipedia.org/wiki/Mangalica

TIL about interactive git staging git add -i

➜  shapehub git:(feature/23869-systematic-therapy) ✗ git add -i
Found existing alias for "git add". You should use: "ga"
           staged     unstaged path
  1:    unchanged       +0/-34 app/views/layouts/application.html.erb
  2:    unchanged       +0/-50 app/views/layouts/croms.html.erb
  3:    unchanged       +0/-30 app/views/layouts/croms/_header.html.erb
  4:    unchanged       +0/-13 app/views/layouts/mailer.html.erb
  5:    unchanged        +0/-1 app/views/layouts/mailer.text.erb

*** Commands ***
  1: status       2: update       3: revert       4: add untracked
  5: patch        6: diff         7: quit         8: help
What now> 2

TIL about custom simpleform inputs: https://github.com/heartcombo/simple_form?tab=readme-ov-file#custom-inputs

class TreeSelectInput < SimpleForm::Inputs::CollectionSelectInput
  def input(wrapper_options)
    super(wrapper_options.merge(data: { controller: "tree-input" }))
  end
end

TIL that an .aiignore file is a thing.

Elasticsearch is also based on Lucene. It means everything I know about Solr still applies.

click_email_link_matching('invivation')

https://github.com/email-spec/email-spec

TIL about Vector ‘retain’ in Rust https://doc.rust-lang.org/std/vec/struct.Vec.html#method.retain