Nomethoderror: Undefined Method 'On' for Main:Object

Undefined method for main:Object (NoMethodError) though method is defined

Ruby expects the method to be declared before you call it, try to move your method definition before you call the method like:

def check_params(param)
 # some code
end

check_params param

NoMethodError: undefined method `on' for main:Object

I had the same error just now after running a bundle update, no major versions were updated, except for Rake to 11. An upgrade from capistrano 3.2.1 to 3.4.0 fixed it for me!

NoMethodError: undefined method `get' for main:Object when I try to install webpacker

I changed the ruby version to the 2.5.6 through rvm and it works.

Thanks to @paulo-felipe-souza!

RSpec NoMethodError: undefined method `describe' for main Object

The solution

Call RSpec.describe instead of just describe.

require 'rspec'
require './RubyOffRailsTuts/classes/furlong'

RSpec.describe Furlong do
end

The reason it works

You can tell from the error message "undefined method `describe' for main Object" that the underlying problem is that you are trying to call describe on the the basic Object main, which does not have a describe method.

Undefined method error for main:Object when using gem

You have defined instance methods, not module methods. Change:

def or_gate(a, b)

to:

def self.or_gate(a, b)

and it'll work the way you expect:

Logic.or_gate(1,2)
 => 1

Repeat this change for all your method definitions.

Alternatively, you can use extend self to accomplish the same goal without having to add self. to each method definition:

module Logic
  extend self

  def or_gate(a, b)
    a || b
  end
end

This adds/copies all the instance methods as module methods.

There is more discussion of this here, and this answer goes into some more detail on how methods are defined in modules.

.select undefined method for main:Object (NoMethodError) Ruby

To get rid of the error just replace array(array.index(value) + 1) with array[array.index(value) + 1].

However the solution will still be incorrect. The method index of an array returns the index of the first object in array such that the object is == to value. In case of duplicate elements in array there will be an error.

I'd recommend rewriting your method as

def remove_double_spaces(array)
  array.join.squeeze(' ').split('')
end

remove_double_spaces([" ", " ", " ", "w", "h", "a", "t", " ", "s", " ", "m", "y", " ", " ", " ", " ", " ", "l", "i", "n", "e", " "])
# => [" ", "w", "h", "a", "t", " ", "s", " ", "m", "y", " ", "l", "i", "n", "e", " "] 

undefined method `each' for main:Object (NoMethodError)

self can't get any values, maybe you are looking for something like gets:

def scrabble
  values = {"a" => 1, "e" => 1, "i" => 1, "o" => 1, "u" => 1}

  list = []

  gets.chomp.split("").each do |letter|
    list << values[letter]
  end

  puts list
end

gets will ask user for input (in console) and with split you convert that input into an array with all characters, then you can use each that array.

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