Get Rid of That Code Smell – Primitive Obsession

Primitive Obsession is described as a common Ruby code smell that appears when Array, String, Fixnum, or Float are used in domain-specific places where they do not fit semantically. The post uses examples such as a string for a URI, a float for money, and a hash for a set of objects, and says the problem is using convenient primitives where a domain object would be more accurate.

Reading notes

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• Primitive Obsession appears when primitive Ruby objects are used intensively in places where their semantics do not match the domain.
• The post says there are no tools it knows of that can reliably detect this smell, so the reader has to rely on domain understanding and manual analysis.
• Monkey patching primitive classes is mentioned as a possible smell indicator.
• The Virtus example shows a Hash being used to represent a set of attributes because it gives easy #[] access.
• The post says that approach is a mistake because the real need is set semantics plus methods to add and merge attributes.
• The replacement in Virtus is Virtus::AttributeSet, a richer object built for attributes.
• AttributeSet exposes a smaller API than Hash and also handles attributes inherited from a parent.
• The closing advice is to use rich domain objects such as Money, Configuration, or GeoLocation instead of spreading primitive values through the code.