Ruby rescue custom exception

Question

In following example:

class Foo class MyCustomerror < StandardError def message "My custom error" end end def self.do_standard 1 / 0 rescue StandardError => e puts e.message end def self.do_custom 1 / 0 rescue MyCustomerror => e puts e.message end end

I have a problem with call rescue block which params is MyCustomerror. If i call Foo.do_standard, rescue block is called, however when i call Foo.do_custom rescue block with MyCustomerror isn't called. Where is the problem?

rescue MyCustomerror rescues MyCustomerror and its subclasses. But ZeroDivisionError isn't one of its subclasses. — Stefan
– Stefan, Commented Nov 16, 2018 at 16:35

Jörg W Mittag · Accepted Answer · 2018-11-16 14:47:53Z

2

There is no place in your code that could raise a MyCustomError exception, so there is nothing to rescue from. The only exception that could possibly be raised by that code is a ZeroDivisionError.

answered Nov 16, 2018 at 14:47

Jörg W Mittag

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5 Comments

Stefan Over a year ago

It might be worth noting that ZeroDivisionError inherits from StandardError which is why rescue StandardError rescues it.

Costy Over a year ago

Place or not place. It does not explain why in case call method do_standard is caught by StandardError, instead in case call do_custom not.

Costy Over a year ago

@Stefan In the above example MyCustomerror is also inherited by StandardError!

David Maze Over a year ago

Both functions raise ZeroDivisionError. ZeroDivisionError is a StandardError so .do_standard rescues it. ZeroDivisionError is not a MyCustomerror and so .do_custom does not rescue it.

Stefan Over a year ago

@user3471671 it's the other way round: MyCustomerror inherits from StandardError. In the class hierarchy, MyCustomerror and ZeroDivisionError are siblings.

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