Anki cards for Ruby

Flashcards for Ruby. Created with Obsidian Anki Sync notation.

[TOC]

default value if variable is `nil`

# number MUST be nil!
# Doesn't work if it's an undefined var.
var = number || 5

default value if argument is not passed

def method(parameter = "default value")
  # ...
end

declare a Class method to be called from the Class name

::
use self.method_name:

class Hello
  def self.world
    "Hello World!"
  end
end

autocreate getters/setters

::
use attr_accessor:

class Person
  attr_accessor :first_name, :last_name
end

what does `String.count` do?

::
counts how many "char-set" there are in the string

>> 'meleu'.count('e')
=> 2
>> 'meleu'.count('el')
=> 3

how `Array.map` works?::

returns a new array with the results of running a block once for every element in the array (enumeration)

# raise all numbers to square
>> [1, 2, 3].map { |num| num ** 2 }
=> [1, 4, 9]

get an array with no repeated items

# use .uniq method
>> [1, 2, 3, 4, 5, 2, 2, 4, 5].uniq
=> [1, 2, 3, 4, 5]

`String.scan` vs. `String.split`?

.scan searches for the items
.split searches for the separators

>> "item1--item2--itemN".split("--")
=> ["item1", "item2", "itemN"]
>> "item1--item2--itemN".split("-")
=> ["item1", "", "item2", "", "itemN"]
>> "item1--item2-:itemN".scan(/item./)
=> ["item1", "item2", "itemN"]

from char to ASCII value

'a'.ord # ordinal
# => 97

from ASCII value to char

97.chr
# => "a"

subtract arrays

[1, 2, 3] - [1, 3]
# => [2]

create an `Array` from a `Range`

# n00b way
alphabet = ('a'..'z').to_a

# ninja way
alphabet = [*'a'..'z']

capture an Exception

begin
  # ... code that can raise an exception...
rescue ExceptionName => e
  # ... code to run when getting an exception
end

How do you clean an `Array` from items matching a condition?

::
Using #reject iterator (think of a negation of #select)

a = [1, 2, 3, 4]
# reject the even numbers:
a.reject { |n| n.even? }
# => [1, 3]

How would you sort an `Array` with a given sorting criteria?

::
Defining the criteria in a block to #sort_by

strings_array.sort_by do |word|
  word.length
end

Anki cards for Ruby

default value if variable is nil