Probably a rethink of the design. Why are you creating an object, then mutating its name from client code?

The whole point of an object is that client code shouldn't be concerned with such details as maintaining the state of each internal field. Try and think of an object as a single thing you send high level messages to you, instead of a struct, or a bag, or a hashtable.

What would a high level message for changing the name of some object look like, if not setName(newName)?

Calls to mutate state, such as changing the name field, should be rare. I don't see the value in adding syntactic sugar to make it easier to mutate state.

"Calls to mutate state, such as changing the name field, should be rare."

Says who?

For example, there is a business requirement that we know the on-hand quantity of some item in the warehouse.

It's a busy warehouse, and we keep picking that item for delivery, and replenishing it from our suppliers.

So, the quantity of the item keeps mutating.

How do you propose to deal with the above? Tell the warehouse people that they should only do their thing "rarely"? Seriously.

He means you'd call `increment(25)` to say you've got 25 more, or `employee.suspend()` instead of `employee.setAccess(SUSPENDED); employee.setPay(0); employee.setBenefits(NONE);`

Increment(25) still mutates the value.

What is the point here?

Point - say you have a database with 300 tables and ~3,000 columns.

You do not want to play the game of "hide the method to change the value". That is a big waste of time for everyone involved.

a guess, but i'd wager "rare" here meant the code should in the main prefer immutable data structures (etc), not that the invocations per unit time of a particular method should be low.

> a guess, but i'd wager "rare" here meant the code should in the main prefer immutable data structures (etc), not that the invocations per unit time of a particular method should be low.

Yeah I want to say that for us developers, "rare" is not something that we can code, without some serious sophistication.

More likely we code "if" and it is either "yes" or no".

To capture "rare", we need some serious tools - statistics, analytics etc etc. That is way beyond the regular developer toolset.

Something like obj.rename(newName). This might seem like a trivial change, but the underlying idea is that we're no longer dealing with a setter only affecting one particular field, but an abstract message that may affect arbitrary internal state.

It would probably look exactly like setName(newName).

For me a better question is - why is the name being changed? What high level goal are you trying to accomplish that truly needs you to to directly mutate internal fields, after the object has already been created? Could the object - or system of objects - have been designed with a higher level interface, so that the outside world didn't have to concern itself with such things?

Things change?

Consider a trivial to-do list. You can click on the 'completed' checkbox. So the 'completed' field has chaged.

Or, you can say ooops I mistyped the label. So you change the label.

Is there anything wrong with that?

I guess not. Sometimes the cleanest thing to do is to just mutate a field - particularly for GUI objects.

I don't know if it's worth the overhead of having unthinking developers writing { get; set } for every field in every class because it makes things "easier".

> I guess not. Sometimes the cleanest thing to do is to just mutate a field - particularly for GUI objects.

I don't know if it's worth the overhead of having unthinking developers writing { get; set } for every field in every class because it makes things "easier".

I do not understand your point. First you claim that we should not mutate the field, then you claim that we should mutate the field.

Which one is it? Mutate or not?

Generally not mutate. And if we must mutate, mutate in a batch with a single method with a descriptive name.

We should generally not use goto or local variables either. Avoid reaching for these constructs first. But if it's by far the cleanest, and simplest way of solving the problem - which it usually isn't - go ahead and do it.

Let's say I have an object representing a file in the file system, and I'm writing a file browser. I give the user the ability to rename the file.

I would say that at that point, it ceases to be a simple setter method (or set property). It's not a simple case of mutating some element of a data structure of filenames as strings. There'd be some validation and error handling involved. It's a perfectly valid high level message to send a file object.

As an aside, I'd probably make a method called "rename" that does this, as opposed to something like "setName".