Ballmerpeak devblog

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Why I like statically typed languages

February 24, 2020 — Richárd Thier

People usually fall into one of the static vs. dynamic languages fanboy group. I always preferred that static languages where types can be determined at the compile time, but I use languages from both worlds. Now I met the kind of error that shines light on why I prefer static languages though. Read on!

Usual reasons to use static vs. dynamic type systems

Pro: using a static type system

  1. You can catch a lot of errors at compile time
  2. Static languages can be made faster
  3. Static languages constrain bad behaviour
  4. Modern static typed languages can infer types anyways (like the C++11 auto keyword)

Pro: using a dynamic type system

  1. Most errors one catches by static type systems are simple errors easy to catch anyways.
  2. Usually performance degrades elsewhere anyways
  3. More freedom, not restrictive, less boiletplate.
  4. Why should I tell what type is that number if the computer can infer it anyways?

But do we really realize what these mean?

My personal insight

The above is well known to most people and it is well visible in flamewars. What does some of the above mean however and why one really likes this or that among the two is not as simple as just listing arguments. The best way to show it is through a good example. I have one now.

Lately I am forking "prosopopee" which is originally a static site generator aimed towards image galleries and photoblogging. I want to make it into a more generic static site generator and use it for my company website. It is python and python is dynamically typed - and the bug I has is typical for it!

    Traceback (most recent call last):
      File "/home/prenex/munka/magosit/python/magosit-website/.venv/bin/prosopopee", line 11, in <module>
        load_entry_point('prosopopee==0.8.2', 'console_scripts', 'prosopopee')()
      File "/home/prenex/munka/magosit/python/magosit-website/.venv/lib/python3.8/site-packages/prosopopee/", line 697, in main
        build_gallery(settings, gallery_settings, gallery_path, templates, galleries_cover=front_page_galleries_cover)
      File "/home/prenex/munka/magosit/python/magosit-website/.venv/lib/python3.8/site-packages/prosopopee/", line 492, in build_gallery
        galleries_cover = sorted([x for x in galleries_cover if x != {}], key=lambda x: x["ord"] if x["ord"] else (x["date"] if x["date"] else x["link"][0]))
    TypeError: '<' not supported between instances of 'str' and ''

This happens when I tried to fix "ordering" of links to subpages. They are called galleries here because of photoblogging terminology. The original app always ordered them according to its date field and because in my case dates do not count I just did not give it in. That ended up crashing the app as it needed this date always in the lambda.

So I changed the lambda to the following one (seen in the Traceback above):

    key=lambda x: x["ord"] if x["ord"] else (x["date"] if x["date"] else x["link"][0]))

Practically I added an ord field and some code to just use the always existing link name when there is no date given in. The most clear case now happens when the user always tells order num using the ord field.

It worked nice, until I got the above exception one day. Why? Oh because I just added ord as user input in the yaml config for my CMS at some of the places, but forgot it at one place where I kept the date. The code thus tried to sort the list of all galleries and once it used the ord field for the ordering and once it used the date field and surely there is no < relation between date and string.

Still the whole thing works in most of the cases magically so it is actually not so easy to reproduce the error. I had hard time to set it up once again to properly reproduce the crash. Also I once got the same crash by making the ord field a number and the link field to be character so there were no < operator between int and str.

Noob error one might say and it is indeed. But the point is that it is not a typo or accident. It is a logic error! A "proper" language can catch this, but a dynamic typing languge let you do this.

As the data is coming from a yaml file the user is editing no linter can ever really warn you for you doing bad things. Also because it works in my case and I know how to use it, one feels much less driving force to "do it right".

I think the last sentence is what makes this dangerous. But I think these kind or errors are not easy to spot at all. No! Do not dare to say!

Tags: static, dynamic, type, language, comparison, which-is-better, rant, reality

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