Why does the Db operations return an unmodifiable list?

[Thomas Hallgren]

I tried to sort a list returned by a Db.list() operation and was
surprised to see that the list was unmodifiable. Why is that? It's a
private copy anyway and modifying it will not cause any harm. Now I
must instead copy the list before I sort it (the sort algorithm is
written in Java and not easy to mimic in SQL).

[John O'Hanley]

It's unmodifiable simply as a defensive measure. That's all. The sort order is important, and is almost always done in the SQL's where-clause.

 - John

[Thomas Hallgren]

I'm all for defensive measures, but what is it that this defends against?

[John O'Hanley]

It defends against inadvertently changing its state.

It just returns the list in an immutable form. Immutables have many benefits (see Effective Java for more details). Many of the classes in web4j are immutable.

Changing the returned list to a mutable form is a one-liner, something like:
List<Thing> newList = new ArrayList<Thing>(oldList);

- John

[Thomas Hallgren]

I'm doing exactly that, but even if it's one single line of code, it does waste both memory and CPU cycles. I'd like to
have a valid reason for doing that.

As I wrote before, I'm all for defensive measures when it has significance. In this case, the preservation of the
'state' of the returned list is completely insignificant nobody else is watching it. The method returns a private list.

- thomas

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