[carterehsmith]

"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.

[arjie]

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);`

[carterehsmith]

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.

[abiox]

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.

[carterehsmith]

> 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.