Does Kotlin have a BigDecimal setPrecision utility method?

Question

I read somewhere that the deciding committee of Java decided that a setPrecision method on BigDecimal would be dumb, since it already has setScale.

What is even dumber is to have API users have methods like this in their code:

private fun getBigDecimalWith16DigitPrecision(value: BigDecimal): BigDecimal {
    return when {
        value < BigDecimal.ONE -> value.setScale(16, RoundingMode.HALF_UP)
        value < BigDecimal(10) -> value.setScale(15, RoundingMode.HALF_UP)
        value < BigDecimal(100) -> value.setScale(14, RoundingMode.HALF_UP)
        value < BigDecimal(1000) -> value.setScale(13, RoundingMode.HALF_UP)
        value < BigDecimal(10000) -> value.setScale(12, RoundingMode.HALF_UP)
        else -> value.setScale(11, RoundingMode.HALF_UP)
    }
}

Which doesn't even cover all cases.

Answer 1

It's just one line, since your scale needs to change by exactly as much as precision does:

fun BigDecimal.setPrecision(newPrecision: Int) = setScale(scale() + (newPrecision - precision()), RoundingMode.HALF_UP)

Or alternatively (more obvious, but less efficient):

fun BigDecimal.setPrecision(newPrecision: Int) = BigDecimal(toPlainString(), MathContext(newPrecision, RoundingMode.HALF_UP))