Ruby: How to convert a string to boolean

Question

If you use Rails 5, you can do ActiveModel::Type::Boolean.new.cast(value).

In Rails 4.2, use ActiveRecord::Type::Boolean.new.type_cast_from_user(value).

The behavior is slightly different, as in Rails 4.2, the true value and false values are checked. In Rails 5, only false values are checked - unless the values is nil or matches a false value, it is assumed to be true. False values are the same in both versions: FALSE_VALUES = [false, 0, "0", "f", "F", "false", "FALSE", "off", "OFF"]

Rails 5 Source: https://github.com/rails/rails/blob/5-1-stable/activemodel/lib/active_model/type/boolean.rb

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

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

Don't think too much:

bool_or_string.to_s == "true"  

So,

"true".to_s == "true"   #true
"false".to_s == "true"  #false 
true.to_s == "true"     #true
false.to_s == "true"    #false

You could also add ".downcase," if you are worried about capital letters.

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

if value.to_s == 'true'
  true
elsif value.to_s == 'false'
  false
end