How Kotlin named arguments might make your code more expressive

One day, I was making unit tests and faced with code like this:

assertEquals(cells[0].left, 100)
assertEquals(cells[0].right, 120)
assertEquals(cells[0].bottom, 200)
assertEquals(cells[1].left, 130)
assertEquals(cells[1].right, 370)
assertEquals(cells[1].bottom, 200)
assertEquals(cells[2].left, 380)
assertEquals(cells[2].top, 380)
assertEquals(cells[2].right, 500)
assertEquals(cells[2].bottom, 200)

The intention of this test is to check the position of every cell. The test checks left, right, and bottom of first two cells. Also, it checks the coordinates of every side of the last cell. The code is clearly understandable, however it looks sloppy. Let’s look how Kotlin can improve it.

fun assertCellPosition(cell: Cell, left: Int? = null, top: Int? = null, right: Int? = null, bottom: Int? = null) {
    left?.let { assertEquals(it, cell.left) }
    top?.let { assertEquals(it, cell.top) }
    right?.let { assertEquals(it, cell.right) }
    bottom?.let { assertEquals(it, cell.bottom) }
}

What you see is a function with: 1) named arguments; 2) default arguments. In the function body, we only check those coordinates which are passed to the function.

Now, we are able to write this

assertCellPosition(cells[0], left = 100, right = 120, bottom = 200)
assertCellPosition(cells[1], left = 130, right = 370, bottom = 200)
assertCellPosition(cells[2], left = 380, top = 380, right = 500, bottom = 200)

This code stays clear, but moreover, get sexy and looks more human readable.