Make your objects immutable by default

More about the Good Dojo

In my post last week, I discussed creating objects that are instantiated safely. Please go back and read if you are interested.

At the end of the post, I mentioned that I'd also written the class so it was immutable when instantiated. This is important!!! I feel like a broken record in repeating this but I am sure at the time of writing your code, you aren't modifying your object all over the place and so are safe in the belief that protecting against mutability is overkill. Please remember though, your code could be around for a hell of a long time. You aren't writing your code for now...

you are writing for the next fool that comes along (including you)

Nothing is more upsetting that coming back to fix a bug on some wonderfully crafted code to say "Who has butchered my code?!", but often you were involved at the start of the process. You made the code easy to modify, allowing objects to be used / reused / modified without thinking of the implications.

The Good Dojo doesn't allow modifications once created.

We allow a Dojo to be created with or without students in the first place but once created, the only public way to access the Students is through an Enumerable which can't be modified. If we want to add a Student we control how the Student is added to the Dojo.

As systems become horrible and a multitude of different devs eventually begin to move your code about and add modifications, your object could end up making it's way all around a code base. Too many times in large systems have I pulled my hair out going down rabbit holes only to find someone had modified an object further down the line where I hadn't expected it or someone had wrapped an if() around some code that was assigning a value to my object (therefore leaving it null).

Again this is all obvious stuff (don't let people change your code without thinking about it). Check your code base, I bet you still have some rofl objects that started life out as "pocos" with { get; set; } on them...


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