Today, another snippet from the category don't try at home, might have unforeseeable consequences! Constant assignment¹ is not permanent in Ruby, so it is perfectly valid to do this: module A end class B def initialize p 42 end end A, B = B, A # warning: already initialized constant A # warning: pre...

In case you have wondered, what this top-level constant TOPLEVEL_BINDING is all about: It is, as its name suggest, the Binding of your script's main scope: a = 42 p binding.local_variable_defined?(:a) # => true p TOPLEVEL_BINDING.local_variable_defined?(:a) # => true def example_method p binding.loc...

What happens when you invoke the Ruby interpreter, even before it executes your first line of code? Actually a lot! A few observations: Initial Load Path These are all locations you can Kernel#require from: $ ruby --disable-all -e 'puts $LOAD_PATH.map{ |path| "- #{path}" }' …/ruby-3.2.0/lib/ruby/sit...

At some point when working with Ruby, you come across this mysterious RbConfig constant. A typical scenario is that you want to check which operating system your current program is executed on. You can do this with RbConfig::CONFIG['host_os'] or RbConfig::CONFIG['arch'], see the RubyGems source for ...

Ruby's Regexp engine has a powerful feature built in: It can match for Unicode character properties. But what exactly are properties you can match for? The Unicode consortium not only assigns all codepoints, it also publishes additional data about their assigned characters. When searching through a ...

When exactly don't you have to :"escape" a Ruby symbol? Because this question is somehow related to the Ruby interpreter's internal usage of symbols, the rules are not the most obvious ones: : + Identifier¹, optionally appended by !, ?, or = (→ methods) :@ + Identifier¹ (→ instance variables) :@@ + ...

A quick reminder that number literals in Ruby can be pretty fancy! Example Evaluates To Class Purpose 0x10 16 Integer Integers in hexadecimal (0-16) format 0o10¹ 8 Integer Integers in octal (0-8) format 0b10 2 Integer Integers in binary (0-1) format 1e1000 Float::INFINITY Float Floats in exponential...

In general, Ruby's reflection capabilities are pretty powerful, although not always logical. However, when reflecting on a method's (or proc's) usage, you are sometimes stuck with sad methods. Sad methods only work for code, that is written in Ruby itself. And Ruby itself (official MRI) is written i...

Programming languages have been, and will always be categorized by their typing system. Naturally, large parts of the Ruby community (including myself) have some kind of aversion against static typing. But while Ruby goes down the route of being dynamically typed that does not mean that you are not ...

ERB stands for <%# Embedded Ruby %> and is the templating engine included in the Ruby Standard Library. While there are more recent gems that provide a better templating experience (see tilt for an abstraction, and erubis/erbse for an updated ERB), it is also convenient to have basic support directl...

Is it a hash? Or is it a hash? hash = {"Idiosyncratic" => "Ruby"} hash["Idiosyncratic"] # => "Ruby" hash.compare_by_identity idiosyncratic_in_variable = "Idiosyncratic" hash[idiosyncratic_in_variable] # => nil hash["Idiosyncratic"] # => "Ruby" Hash#compare_by_identity changes the semantics of what i...

RubyGems is bundled with core Ruby since 1.9, which was first released in 2007. As long as you do not run Ruby with the $ ruby --disable-gems flag, it is available to you without having to install anything. This also means that you can use some of RubyGems' support utilities for free! 1) Current Pla...

Ruby's syntax is so expressive — it utilizes every printable, non-alphanumeric ASCII character as much as it cans. Sometimes, this can be confusing for beginners. The next sections show 4+ different meanings of every portrayed single character (not counting different meaning as custom string delimit...

If you don't like errors in your code, you will have to fix them. This handy list of Ruby's errors will hopefully help you do so! (And welcome back for the second season of Idiosyncratic Ruby!) Built-in Exceptions Exception Thrown by core Ruby when Remarks NoMemoryError The Ruby interpreter could no...

This is a summary of reasons why you should still use Ruby: It is a language with a terrific community (welcoming and always questioning itself) and ecosystem (a lot of problems already solved), which is beautiful (focus on productivity), a little conservative (in the sense that it is easy to work w...

Ruby's regex engine defines a lot of shortcut character classes. Besides the common meta characters (\w, etc.), there is also the POSIX style expressions and the unicode property syntax. This is an overview of all character classes: Meta Chars Char Negation ASCII Unicode . - ¹ Any ¹ Any \X - Any Gra...

If you take a closer look, you'll notice that Ruby's grammar has quite a few edge-case where its syntax is inconsistent or ambiguous: Binary Minus vs Minus taken as Unary Method Argument >> [1,3,4,5].size - 1 # => 3 >> [1,3,4,5].size -1 # wrong number of arguments(1 for 0) No Simple Rule, if a Symbo...

There is an operator in Ruby, that does nothing: The unary plus operator. It is part of the language for keeping symmetry with the unary minus operator! This is awesome, an operator for free! How can we utilize it? Update: In Ruby 2.3, the plus operator got its first purpose: Create an unfrozen copy...

Code Golf is the art of writing the shortest program possible. The less bytes the better. And the competition is just ridiculously strong! Head over to Anarchy Golf if you want to see more! A good beginner's problem is printing out Pascal's Triangle: Spend a few days to get to 45 bytes. Spend a few ...

Ruby has three default encodings. One of them is the default source encoding, which can be set using a magic comment in the file's first line, or in the second line if the first line is taken by a shebang. Default source encoding (UTF-8): p "".encoding #=> #<Encoding:UTF-8> With encoding comment (fi...

Ruby clutters its objects a lot with methods for metaprogramming other methods: Class.instance_methods.grep /method/ => [:instance_methods, :public_instance_methods, :protected_instance_methods, :private_instance_methods, :method_defined?, :public_method_defined?, :private_method_defined?, :protecte...

If you change one line in Ruby's source, it will support goto statements! You can install a patched version via RVM's patch feature: $ rvm install 2.2.2 -n goto --patch http://git.io/vfxF2 $ rvm use 2.2.2-goto What to do to play around with this new feature? Let's reimplement this famous bug in Ruby...

Tired of good old, but slow Ruby? Try one of Ruby's successors: Name Compiles To Description Crystal Machine Fast Ruby Mirah JVM Fast Ruby in Java Opal JS Ruby for JavaScript CoffeeScript JS JavaScript for Rubyists Elixir BEAM Ruby for Erlang Scala JVM Multi-Paradigm Ruby Rooby Machine Simple Ruby R...

Ruby has a built-in feature that is much like Literate CoffeeScript. In contrast to it, this Ruby option will not ignore literature, but garbage: -x[directory] Tells Ruby that the script is embedded in a message. Leading garbage will be discarded until the first line that starts with “#!” and contai...

Ruby's URI standard library contains a very sophisticated regex for matching URLs: "At https://idiosyncratic-ruby.com you can learn about the " \ "obscure parts of Ruby"[URI.regexp] # => "https://idiosyncratic-ruby.com" This regex is built in uri/rfc2396_parser.rb and looks like this: $ ruby -v ruby...

A guide to Ruby's stdlib and available alternatives. Please note: The standard library was turned into gems, see stdgems.org for up-to-date information on all standard gems! Standard Library Overview Library Sources Description Alternatives abbrev mri Small library that finds the shortest abbreviati...

This episode takes a look at the unusual use of symbols in one of Ruby's core APIs: Enumerable#chunk The chunk method splits the receiver object into multiple enumerators, using the rule defined in the block. It keeps together the parts that match in series. It then passes the result of this rule an...

Ruby's Struct class is a convenient way to create Ruby classes, which already have some attributes defined. If you are not familiar with structs, you should watch Avdi Grimm's introduction to structs! But in many cases there is something better than structs: Gems that Define Attributes for "Plain Ol...

One of Ruby's goals was to replace popular unix stream editors like awk or sed, which both have the concept of manipulating files in a line-based manner. Ruby has the -n option for this: Causes Ruby to assume the following loop around your script, which makes it iterate over file name arguments some...

Ruby allows you to change key functionality of the language. This means, it is also possible to break key functionality! Six examples of Ruby code you should never use: Undefining Core Methods The simplest way to change Ruby's global behavior is monkey patching: Nothing stops you from altering impor...