original_string: public function boolean()
      {
          $message = ['%s is {{not|}} a boolean', $this->value];
          $this->assert(is_bool($this->value), $message);
  
          return $this;
      }
code: public function boolean()
      {
          $message = ['%s is {{not|}} a boolean', $this->value];
          $this->assert(is_bool($this->value), $message);
  
          return $this;
      }
code_tokens: public function boolean ( ) { $ message = [ '%s is {{not|}} a boolean' , $ this -> value ] ; $ this -> assert ( is_bool ( $ this -> value ) , $ message ) ; return $ this ; }
docstring: Assert that the value is a boolean type.
  
  @throws AssertionFailureException
  
  @return self
docstring_tokens: Assert that the value is a boolean type .