Advent of Mistakes

Update: The solutions (without these mistakes) can be found in this repo: meadsteve/advent-of-code-2020

For this year’s advent of code I decided to try a new language: crystal. I wanted to write about the challenges I’ve faced writing in a language new to me.

Frustrating bugs

Here are some of the mistakes I made (often more than once) whilst working with this new language.

assignment (=) when I meant equality check (==)

I had a block of code like this:

  if char == 'F'
    row_range = row_range.lower_half
  elsif char = 'B'
    row_range = row_range.upper_half
  elsif char = 'L'
    col_range = col_range.lower_half
  elsif char = 'R'
    col_range = col_range.upper_half
  end

It took me a longer than I’d care to admit to notice that the second if was mutating the value of char. I’d love to have some immutability in the language here to help me not fall into this trap. Maybe it has that? Maybe it has some patterns

Forgetting constructors are .new

My current day job is writing python where constructing a new class looks like this MyNewClass(data). In crystal it’s MyNewClass.new(data). It’s taking my muscle memory a while to learn this. In addition MyNewClass(data) can mean something in crystal but it’s not construction of a new object.

Overriding a method in the same class :facepalm:

I wrote code like this (I’ve abridged for clarity):

  class ThingDoer
    def my_very_important_thing
       false
    end
    
    def my_very_important_thing
       true
    end
  end

I did not realise it was possible for a function to be overwritten in the same definition of a class. Took me a while to spot this silly mistake. I wonder what the use case for this is.

' for chars and " for strings

I was iterating over "some_string".chars and I wondered why this if statement was never true char == "F". The .chars function returns charecters as an enumerable which means I needed to compare it to 'F' which is the charecter F not "F" which is a string made up of a single F.

Non-idomatic Code

The harder thing is the feeling that the code I’m writing is clumsy and not embracing the language yet. I think the solution here would be spending more time reading Crystal (and probably) ruby code.

Thoughts? Comments? Send me a tweet!
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