$ pry
>> class String
 |   def to_bool
 |     raise RuntimeError, 'Go fuck yourself' unless ['true', 'false'].include?(self)
 |     self == 'true'
 |   end
 | end
:to_bool
>> 'true'.to_bool
true
>> 'false'.to_bool
false
>> 'shit'.to_bool
RuntimeError: Go fuck yourself
from (pry):3:in `to_bool'
>> # or more simplistic way
>> le_string = 'true'
"true"
>> (le_string == 'true')
true
>> le_string = 'false'
"false"
>> (le_string == 'true')
false
>>