Ruby: How to convert a string to boolean

Question

I have a value that will be one of four things: boolean true, boolean false, the string \"true\", or the string \"false\". I want to convert the string to a boolean if it i

Answer 1

In Rails I prefer using ActiveModel::Type::Boolean.new.cast(value) as mentioned in other answers here

But when I write plain Ruby lib. then I use a hack where JSON.parse (standard Ruby library) will convert string "true" to true and "false" to false. E.g.:

require 'json'
azure_cli_response = `az group exists --name derrentest`  # => "true\n"
JSON.parse(azure_cli_response) # => true

azure_cli_response = `az group exists --name derrentesttt`  # => "false\n"
JSON.parse(azure_cli_response) # => false

Example from live application:

require 'json'
if JSON.parse(`az group exists --name derrentest`)
  `az group create --name derrentest --location uksouth`
end

confirmed under Ruby 2.5.1

Answer 2

I've frequently used this pattern to extend the core behavior of Ruby to make it easier to deal with converting arbitrary data types to boolean values, which makes it really easy to deal with varying URL parameters, etc.

class String
  def to_boolean
    ActiveRecord::Type::Boolean.new.cast(self)
  end
end

class NilClass
  def to_boolean
    false
  end
end

class TrueClass
  def to_boolean
    true
  end

  def to_i
    1
  end
end

class FalseClass
  def to_boolean
    false
  end

  def to_i
    0
  end
end

class Integer
  def to_boolean
    to_s.to_boolean
  end
end

So let's say you have a parameter foo which can be:

• an integer (0 is false, all others are true)
• a true boolean (true/false)
• a string ("true", "false", "0", "1", "TRUE", "FALSE")
• nil

Instead of using a bunch of conditionals, you can just call foo.to_boolean and it will do the rest of the magic for you.

In Rails, I add this to an initializer named core_ext.rb in nearly all of my projects since this pattern is so common.

## EXAMPLES

nil.to_boolean     == false
true.to_boolean    == true
false.to_boolean   == false
0.to_boolean       == false
1.to_boolean       == true
99.to_boolean      == true
"true".to_boolean  == true
"foo".to_boolean   == true
"false".to_boolean == false
"TRUE".to_boolean  == true
"FALSE".to_boolean == false
"0".to_boolean     == false
"1".to_boolean     == true
true.to_i          == 1
false.to_i         == 0

Answer 3

Although I like the hash approach (I've used it in the past for similar stuff), given that you only really care about matching truthy values - since - everything else is false - you can check for inclusion in an array:

value = [true, 'true'].include?(value)

or if other values could be deemed truthy:

value = [1, true, '1', 'true'].include?(value)

you'd have to do other stuff if your original value might be mixed case:

value = value.to_s.downcase == 'true'

but again, for your specific description of your problem, you could get away with that last example as your solution.

Answer 4

Working in Rails 5

ActiveModel::Type::Boolean.new.cast('t')     # => true
ActiveModel::Type::Boolean.new.cast('true')  # => true
ActiveModel::Type::Boolean.new.cast(true)    # => true
ActiveModel::Type::Boolean.new.cast('1')     # => true
ActiveModel::Type::Boolean.new.cast('f')     # => false
ActiveModel::Type::Boolean.new.cast('0')     # => false
ActiveModel::Type::Boolean.new.cast('false') # => false
ActiveModel::Type::Boolean.new.cast(false)   # => false
ActiveModel::Type::Boolean.new.cast(nil)     # => nil

Answer 5

In rails, I've previously done something like this:

class ApplicationController < ActionController::Base
  # ...

  private def bool_from(value)
    !!ActiveRecord::Type::Boolean.new.type_cast_from_database(value)
  end
  helper_method :bool_from

  # ...
end

Which is nice if you're trying to match your boolean strings comparisons in the same manner as rails would for your database.

Answer 6

def true?(obj)
  obj.to_s.downcase == "true"
end