Implement array expressions

[katcharov]

JAVA-4805

[jyemin]

LGTM

[stIncMale]

[optional]
Given that distinct is implemented via setUnion, the order of elements in the produced array is undefined, but it's not unreasonable for a user to expect that the order is preserved. Can you think of ways to express the undefined order via the method name? For example, the name set() implies that the result has neither duplicates nor a defined order.

[katcharov]

Perhaps union should exclude set in its name instead, and the docs should cover this?

The name set seems confusing because of setField, and asSet implies another type. I do not think distinct implies that items will remain in the same order, like for example removeDuplicates might.

[stIncMale]

If we look at SQL, what we call setUnion is called union there. However, what is called distinct in SQL preserves the order, unlike what we call distinct here. I.e., distinct may be seen as implying order.

If you don't see a way to simply and clearly express the lack of order in the names, it's fine, neither do I.

As for setUnion vs union - given that we don't express the lack of order in the name of distinct, I am also fine with union.

[katcharov]

I confirmed that this does not preserve order even when there is only one set in the union:

        assertExpression(
                Arrays.asList(1, 2, 3),
                ofIntegerArray(3, 2, 1, 3, 3, 3).distinct(),

passes. I agree that given what you say, distinct will imply they remain in the same order for users familiar with SQL distinct. And even the streams distinct specifies that if it is ordered, it will remain ordered. But the two other points (setField is weird, implies other type) still seem compelling. Maybe some variation of "unique" instead?

[stIncMale]

I am fine with unique. If you leave distinct, I can also live with that.

[stIncMale]

Leaving a comment so that stupid GitHub allowes me to finish the review despite my having left comments in existing discussions.