GitLab Documentation

GitLab utilities

GitLab utilities

We developed a number of utilities to ease development.

MergeHash

  • Deep merges an array of hashes:

    Gitlab::Utils::MergeHash.merge(
      [{ hello: ["world"] },
       { hello: "Everyone" },
       { hello: { greetings: ['Bonjour', 'Hello', 'Hallo', 'Dzien dobry'] } },
        "Goodbye", "Hallo"]
    )
    

    Gives:

    [
      {
        hello:
          [
            "world",
            "Everyone",
            { greetings: ['Bonjour', 'Hello', 'Hallo', 'Dzien dobry'] }
          ]
      },
      "Goodbye"
    ]
    
  • Extracts all keys and values from a hash into an array:

    Gitlab::Utils::MergeHash.crush(
      { hello: "world", this: { crushes: ["an entire", "hash"] } }
    )
    

    Gives:

    [:hello, "world", :this, :crushes, "an entire", "hash"]
    

Override

  • This utility could help us check if a particular method would override another method or not. It has the same idea of Java's @Override annotation or Scala's override keyword. However we only do this check when ENV['STATIC_VERIFICATION'] is set to avoid production runtime overhead. This is useful to check:

    • If we have typos in overriding methods.
    • If we renamed the overridden methods, making original overriding methods overrides nothing.

    Here's a simple example:

    class Base
      def execute
      end
    end
    
    class Derived < Base
      extend ::Gitlab::Utils::Override
    
      override :execute # Override check happens here
      def execute
      end
    end
    

    This also works on modules:

    module Extension
      extend ::Gitlab::Utils::Override
    
      override :execute # Modules do not check this immediately
      def execute
      end
    end
    
    class Derived < Base
      prepend Extension # Override check happens here, not in the module
    end
    

StrongMemoize

  • Memoize the value even if it is nil or false.

    We often do @value ||= compute, however this doesn't work well if compute might eventually give nil and we don't want to compute again. Instead we could use defined? to check if the value is set or not. However it's tedious to write such pattern, and StrongMemoize would help us use such pattern.

    Instead of writing patterns like this:

    class Find
      def result
        return @result if defined?(@result)
    
        @result = search
      end
    end
    

    We could write it like:

    class Find
      include Gitlab::Utils::StrongMemoize
    
      def result
        strong_memoize(:result) do
          search
        end
      end
    end
    
  • Clear memoization

    class Find
      include Gitlab::Utils::StrongMemoize
    end
    
    Find.new.clear_memoization(:result)
    

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