Module ActiveSupport::Rescuable

     # File activesupport/lib/active_support/rescuable.rb, line 85
 85:     def handler_for_rescue(exception)
 86:       # We go from right to left because pairs are pushed onto rescue_handlers
 87:       # as rescue_from declarations are found.
 88:       _, rescuer = self.class.rescue_handlers.reverse.detect do |klass_name, handler|
 89:         # The purpose of allowing strings in rescue_from is to support the
 90:         # declaration of handler associations for exception classes whose
 91:         # definition is yet unknown.
 92:         #
 93:         # Since this loop needs the constants it would be inconsistent to
 94:         # assume they should exist at this point. An early raised exception
 95:         # could trigger some other handler and the array could include
 96:         # precisely a string whose corresponding constant has not yet been
 97:         # seen. This is why we are tolerant to unknown constants.
 98:         #
 99:         # Note that this tolerance only matters if the exception was given as
100:         # a string, otherwise a NameError will be raised by the interpreter
101:         # itself when rescue_from CONSTANT is executed.
102:         klass = self.class.const_get(klass_name) rescue nil
103:         klass ||= klass_name.constantize rescue nil
104:         exception.is_a?(klass) if klass
105:       end
106: 
107:       case rescuer
108:       when Symbol
109:         method(rescuer)
110:       when Proc
111:         rescuer.bind(self)
112:       end
113:     end

    # File activesupport/lib/active_support/rescuable.rb, line 78
78:     def rescue_with_handler(exception)
79:       if handler = handler_for_rescue(exception)
80:         handler.arity != 0 ? handler.call(exception) : handler.call
81:         true # don't rely on the return value of the handler
82:       end
83:     end