Immutability

I am a paid up member of the immutability appreciation society. I believe programming in an immutable language reduces bugs, as well as potentially helps the compiler optimise your code (though perhaps at the cost of not being able to do similar optimisations yourself). I also rather suspect that immutability has a role to play in concurrent code, but that’s somewhat irrelevant for today. However, although I feel that immutability reduces bugs, I do not think of it as a strict subset. A strict subset would imply both that, some bugs introduced using a mutable language are simply not possible, or at least less likely when using an immutable language and also there are no bugs introduced using an immutable language that would be impossible or less likely when using a mutable language. It’s the second part I disagree with. I think most immutable programmers know this, but it’s worth reminding ourselves of this. It’s very easy to get comfortable in our land of the fewer bugs. ...