ActiveSupport::Rescuable

     # File lib/active_support/rescuable.rb, line 84
 84:     def handler_for_rescue(exception)
 85:       # We go from right to left because pairs are pushed onto rescue_handlers
 86:       # as rescue_from declarations are found.
 87:       _, rescuer = self.class.rescue_handlers.reverse.detect do |klass_name, handler|
 88:         # The purpose of allowing strings in rescue_from is to support the
 89:         # declaration of handler associations for exception classes whose
 90:         # definition is yet unknown.
 91:         #
 92:         # Since this loop needs the constants it would be inconsistent to
 93:         # assume they should exist at this point. An early raised exception
 94:         # could trigger some other handler and the array could include
 95:         # precisely a string whose corresponding constant has not yet been
 96:         # seen. This is why we are tolerant to unknown constants.
 97:         #
 98:         # Note that this tolerance only matters if the exception was given as
 99:         # a string, otherwise a NameError will be raised by the interpreter
100:         # itself when rescue_from CONSTANT is executed.
101:         klass = self.class.const_get(klass_name) rescue nil
102:         klass ||= klass_name.constantize rescue nil
103:         exception.is_a?(klass) if klass
104:       end
105: 
106:       case rescuer
107:       when Symbol
108:         method(rescuer)
109:       when Proc
110:         rescuer.bind(self)
111:       end
112:     end

    # File lib/active_support/rescuable.rb, line 77
77:     def rescue_with_handler(exception)
78:       if handler = handler_for_rescue(exception)
79:         handler.arity != 0 ? handler.call(exception) : handler.call
80:         true # don't rely on the return value of the handler
81:       end
82:     end