Mailinglist Archive: yast-devel (31 mails)

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Re: [yast-devel] Again: 98% of "undefined method" errors have nothing to do with static typing
On Wed, Dec 13, 2017 at 12:18:16AM +0100, Ancor Gonzalez Sosa wrote:
This is probably the less useful mail ever, since it just goes over a
topic that has been explained over and over and still pops us in almost
every single meeting.

Let me say it again: 98% of the "undefined method `xxx' for
nil:NilClass" errors are NOT related AT ALL to Ruby being dynamically
typed and would NOT be prevented by the usage of a statically typed

And the other side of the same recurring coin - we don't write unit
tests as a replacement for the compiler checks. That's not the point,
the goal or the intention of the unit tests.

This time I will try to explain it with an example (something that
already has been done, but I just felt impelled to do it one more time).

Let's say you have this Ruby method that returns an object of type
Device or nil if the device was not found


And then you write this code

dev = find_device_by_name("/dev/sda")
puts dev.size

If there is no /dev/sda that will result in one of those "undefined
method `size` for nil:NilClass" that some people hate so much. Did it
happen because Ruby is dynamically typed? NOT AT ALL. It happened
because you didn't check for the situation in which the device is not
there with some code like this.

dev = find_device_by_name("/dev/sda")
if dev
puts dev.size
puts "No such device"

Let's do the same in an hypothetical typed Ruby in which there is
nothing like nil. Now your find_device_by_name method will raise a
NotFound exception instead of returning nil if the device is not there
(the approach we use in statically typed languages).

The first example will still fail, now with an uncaught NotFound
exception. The static type checking performed by the compiler didn't
save us from THE DEVELOPER ERROR and the result is pretty much the same
- an exception thrown in the user's face.

I think you are mixing static typing and static code analysis.

ciao Arvin

Arvin Schnell, <aschnell@xxxxxxxx>
Senior Software Engineer, Research & Development
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284
(AG Nürnberg)
Maxfeldstraße 5
90409 Nürnberg
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