Does anyone have preferred ways to handle when you...

# codingconventions

[smichel17]

Does anyone have preferred ways to handle when you either want a thing, or that same thing with some action applied to it? Or a name for that pattern.

val distinct: Boolean
val list: List<T>
val maybeDistinct = if (distinct) list.distinct() else list

It's similar to takeUnless , but without the intermediary null, which makes it kind of ridiculous

val maybeDistinct = list.takeUnless { distinct } ?: list.distinct()

I could write an extension function, something like

val maybeDistinct = list.transformIf(distinct) { it.distinct() }

…which in this case is just as verbose, but has nicer signaling, imo. Maybe there's a stdlib function like this that I don't know about?

[smichel17]

Not totally sure if this counts as a coding convention, but there's no #idioms

[hho]

There's #codereview – I'd say, the simple if is the winner: Cleanest, easiest to understand and shortest code!

[smichel17]

I'll do #codereview next time, thanks. In this simple example I think I agree with you. But—

It doesn't chain as nicely. You need a

.let { if (distinct) it.distinct() else it }

vs

.transformIf(distinct) { it.distinct() }

(also, could be a shorter name, like applyIf or mapIf)

[smichel17]

It's also more awkward with longer variable names or if you need a line wrap. Here's a real-world usage I'm looking at

private fun moveFavouritesToFront(originalList: List<DisplayItem<I>>): List<DisplayItem<I>> {
    return if (originalList.size > itemsPerRow && moveFavoritesToFront) {
        favs.moveLastPickedDisplayItemsToFront(javaClass.simpleName, originalList, originalList)
    } else {
        originalList
    }
}

[smichel17]

vs something like

private fun moveFavouritesToFront(originalList: List<DisplayItem<I>>): List<DisplayItem<I>> {
    originalList.transformIf(originalList.size > itemsPerRow && moveFavoritesToFront) {
        favs.moveLastPickedDisplayItemsToFront(javaClass.simpleName, it, it)
    }
}

[smichel17]

The easiest for me to follow would be

if (!distinct) list else list.distinct()

but this requires inverting the condition :/

[smichel17]

because,

private fun moveFavouritesToFront(originalList: List<DisplayItem<I>>): List<DisplayItem<I>> {
    return if (!(originalList.size > itemsPerRow && moveFavoritesToFront)) originalList
        else favs.moveLastPickedDisplayItemsToFront(javaClass.simpleName, originalList, originalList)
}

is good too, except for the awkward inversion

[elizarov]

#stdlib

[Youssef Shoaib [MOD]]

I've personally defined a letIf function sometimes that does practically the same thing.