Avoiding anti-patterns in Ruby - Arrays

Posted on | 985 words | ~5mins

Since I came to Ruby from the Java and PHP world I’ve found many expressions used in Ruby cryptic and I’ve been trying to avoid them in my daily life. After years and thousand lines of Ruby code I’ve read, I feel a need to change the way I write the code. I want to make my code look better, readable and preferably save some keystrokes.

In software engineering, an anti-pattern (or antipattern) is a pattern that may be commonly used but is ineffective and/or counterproductive in practice. wikipedia

For, each or map?

Iteration is the perfect example of what I should improve. When I started writing the Ruby code, I was used to write constructions like this:

This is syntactically perfect Ruby code. Also for the PHP/Java newcomers it looks perfectly safe. However, it’s not what the rest of the Ruby programmers usually write. As you may already know, Ruby is an object-oriented language and [] in Ruby is just an alias for the Array.new. If you look to the Array class documentation, you will find many interesting methods I want to describe below:


The ’each’ method can be used for iterating the Array in case you don’t want to return anything from the iteration block:

This method is good if you want to modify some object outside the iteration block, or just call some method without caring to much about what the method returns, like:

For example, you can create an alias in Array for .each:

This will immediately yell on you what this code is trying to do. Please do not use this method for changing the content of variables or creating new arrays.

In most cases, the .each method can be replaced with some of the methods bellow:


There are cases when you want to modify the content of an Array and return the modified content. In PHP, you usually do a clone of the Array or create a new array with updated items. In Ruby this is not necessary:

As you may guess, there are few glitches in this code. First, you create a new variable (mean you allocate space for it). In many cases you also leave the variable a abandoned, stealing your memory quietly. The right Ruby approach is to use the .map method:

The .map method here iterates through array and gives you chance to modify the content of it. Then it returns the modified Array back to you, but keeps the original content of a variable untouched. If you don’t want to return anything, but just want to modify the original array instead, use the .map! method:


The next anti-pattern commonly seen by Ruby newcomers, is to use .each to iterate through the Array and return a boolean when it finds a match:

Please keep in mind that the return statement is used only for returning from a method or Proc/lambda. And you should then use this statement in the context of this method, not in the context of the .each block. The correct Ruby approach here would be to use the any? method to search the array:

The example above returns true if there is an odd number in the array. No need to write over-complicated .each iterations.

The ultimate main goal of every Ruby programmer who care about the code he is writing is to make the reader of his code understand what the author is trying to say (without using comments). Ruby offers many ‘syntax’ sugar methods to achieve this goal. For example:

As you can see, Ruby is trying to be very descriptive for the reader, so you don’t need to read too much code to get a clue what the code is trying to do.

There are many aliases that can help you to make your code more readable. For example the .index method, that will return a position of the element inside the Array is just an alias for the .find_index method. If it makes your code more readable, you’re free to use this alias instead of the original method.

In Ruby Array class you can find more handy aliases. For example if you want to access first or last item of the array, you can think about writing this:

Since the indexing of arrays in Ruby starts from zero, the programmer may know that you’re trying to access first element. But why make people think about indexing numbers? For example, you can use the .first method in Array to retrieve the first item. In this case, it doesn’t really matter what is the index number of first element:

The same thing applies for the last item in array. As you might see in the first example, the calculation is quite strange and it does not yell on you that you want to return the last element. So there is the .last method that will hide this calculation for you and yell on the reader that you want to access the last element.

So a quick summary:

  • Use the .each method only when you’re not modifying any variable in the current context. Modifying the state of an object using exclamation mark methods is perfect use-case for this.

  • Use .map when you need to modify content of a variable or return a modified version of the array. This method has also an alias .select. Use it if it makes your code more readable.

  • Use .any? when you’re searching for an item in the array that matches to given condition. If you’re doing a simple search, you can also proceed with .include?

  • Look to the Array docs every time you’re doing something nasty with .each. There will always be a method that will do better a job with less amount of code.

  • Try to avoid accessing elements in array using the array index. If you want to get the last or first item, there is a helper for that.