11 Ruby Tricks You Haven’t Seen Before

Looking for some cool Ruby tricks?

You found them!

In this article I want to share with you some of my favorites.


Deep copy

When you copy an object that contains other objects, like an Array, only a reference to these objects is copied.

You can see that in action here:

food = %w( bread milk orange )
food.map(&:object_id)       # [35401044, 35401020, 35400996]
food.clone.map(&:object_id) # [35401044, 35401020, 35400996]

Using the Marshal class, which is normally used for serialization, you can create a ‘deep copy’ of an object.

def deep_copy(obj)

The results:

deep_copy(food).map(&:object_id) # [42975648, 42975624, 42975612]

Different ways to call a lambda

my_lambda = -> { puts 'Hello' }


If possible, you should stick with the first one (call), because it’s the one most people know.

Creating a pre-filled array

The Array class can take an argument + a block, which lets you create an array with n elements. By default these elements are nil, but if you have a block, the values will come from it.


Array.new(10) { rand 300 }

This will generate an array with 10 random numbers which are between 0 and 299.

True, false and nil are objects

true.class  # TrueClass
false.class # FalseClass
nil.class   # NilClass

There is only one copy of these objects, and you can’t create more even if you wanted.

This is the singleton pattern in action.

Lambdas are strict about arguments, but Procs don’t care

my_lambda = ->(a, b)  { a + b }
my_proc   = Proc.new  { |a, b| a + b }

# ArgumentError: wrong number of arguments (1 for 2)

# TypeError: nil can't be coerced into Fixnum

Execute code directly without irb or files

The ruby command has a number of interesting options you can use.

For example, with the -e flag you can pass in a snippet of code to be executed.

ruby -e '5.times { puts "Fun with Ruby" }'

You can find more by using the -h flag.

Your own mini-irb in one command

Ever wanted to know how irb works? Well, this is a super-simple version of it.

Remember what ‘REPL’ stands for: Read-Eval-Print Loop.

ruby -n -e 'p eval($_)'

You won’t get a prompt, but go ahead and type some Ruby code.

"A" * 5

This works because the -n flag does this:

-n    assume 'while gets(); ... end' loop around your script

And $_ is a global variable. Which contains the following:

The last input line of string by gets or readline.

Unfreeze an object (danger!)

There isn’t any Ruby method to unfreeze an object, but using the Fiddle class you can reach into Ruby internals to make it happen.

require 'fiddle'

str = 'water'.freeze
str.frozen? # true

memory_address = str.object_id * 2

Fiddle::Pointer.new(memory_address)[1] &= ~8

str.frozen? # false

Don’t try this at home!

Objects with special identity

Ruby objects have an identifier or ‘id’ number you can access using the object_id method. Some objects have a fixed id: Fixnums, true, false & nil.

false.object_id # 0
true.object_id  # 2
nil.object_id   # 4

1.object_id # 3
2.object_id # 5

Fixnum ids use this formula: (number * 2) + 1.

Bonus: The maximum Fixnum is 1073741823, after that you get a Bignum object.

Avoid big output in irb or pry

If you are working in irb and want to avoid filling your screen with the contents of some really big array or string you can just append ; at the end of your code.


require 'rest-client'


Try again without the ; to see the difference πŸ™‚

Using the caller method to get the current call stack

Here is a code example:

def foo

def bar
  puts caller



-:3:in 'foo'
-:10:in '<main>'

If you need the current method name you can use __method__ or __callee__.

Bonus! Convert any value into a boolean

!!(1)   # true
!!(nil) # false

Bonus! Use A Keyword As A Variable Name

def foo (if: nil)

foo(if: true)


I hope you enjoyed these Ruby tricks!

Share them with you friends so they can enjoy them too & subscribe to my blog in the form below so you won’t miss my next post. πŸ™‚

21 thoughts on “11 Ruby Tricks You Haven’t Seen Before”

  1. Thanks, Jesus!
    I like your blog πŸ™‚
    Just want to add a little detail to trick 10: I think that just putting ‘;’ after any ruby code will suppress the output.

    • But in (my) irb, just leaving a trailing ; will not execute the expression. It is now waiting for another expression on a new line. I usually append ‘;nil’.
      Maybe there is another dependency (readline?) in play.

  2. My inner troll politely asks, “What happens when you deep clone objects which are actually just wrappers over external resources, i.e. sockets, file handles, db connections, etc.?”

    • That’s an interesting question πŸ™‚

      I just ran a quick test and the answer is simple: Ruby won’t let you do it.

      I tried with a socket and I get: TypeError: can't dump TCPSocket.

  3. For #1, for a simple string array, we could also use the following.


    May be, if the objects are deep by multiple levels, marshaling could be a way.

  4. Here’s another one for your list… a little gem which uses Fiddle to access an otherwise internal-only part of Ruby itself to access the bindings of any caller of a function. If a calls b, which calls c, which calls d… then the ‘bindings’ gem will allow the d method to access variables defined in c, b, or a. The code is tiny and has been extremely helpful for us!

    Check it out at: https://github.com/shreeve/bindings

  5. “Bonus: The maximum Fixnum is 1073741823, after that you get a Bignum object.”
    Only for 32-bit systems.

Comments are closed.