Those who are working on High Available systems/databases consider Redundancy as one of the possible ways to achieve high availability. Redundancy in this case is helping in positive way. But consider the other side of it- In a high available database systems the data is replicated across different nodes. Any change/update at one node has to be propagated to all other nodes, failure during replication can cause mismatch in the data at different nodes. This shows redundancy is both good and bad. But why I am writing about high available systems when the title says “good code”. Because when it comes to redundancy in code- there is NO goodness in it.
The most common tendency of every programmer is to Copy-Paste. I remember reading somewhere that programmers have to be lazy, but where ever I read it the author didn’t mean that being lazy is to Copy-Paste. Instead its to write code which is concise and clear. One of the possible reasons why we tend to Copy-Paste is because the design of the existing code doesn’t facilitate reuse. Now any change to code at one place would trigger same change at multiple places. This is one of the most common ways of introducing redundancy.