[移动开发]kotlin 中的takeif和takeunless的使用

1、takeIf的源码

/**
 * Returns `this` value if it satisfies the given [predicate] or `null`, if it doesn't.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#takeif-and-takeunless).
 */
@kotlin.internal.InlineOnly
@SinceKotlin("1.1")
public inline fun <T> T.takeIf(predicate: (T) -> Boolean): T? {
    contract {
        callsInPlace(predicate, InvocationKind.EXACTLY_ONCE)
    }
    return if (predicate(this)) this else null
}

2、takeUnless的源码

/**
 * Returns `this` value if it _does not_ satisfy the given [predicate] or `null`, if it does.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#takeif-and-takeunless).
 */
@kotlin.internal.InlineOnly
@SinceKotlin("1.1")
public inline fun <T> T.takeUnless(predicate: (T) -> Boolean): T? {
    contract {
        callsInPlace(predicate, InvocationKind.EXACTLY_ONCE)
    }
    return if (!predicate(this)) this else null
}

3、实际应用中的用法

fun uotation(params: QuotationParam, companyCode: String?) = coroutineScope {
		val exchangeDate = LocalDate.now() //前端没有传递参数，默认为调用当天的汇率
		val exchangeDto = companyCode?.takeUnless { it.isBlank() }
			?.let { company ->
				XXX.getExchangeWithCompanyCode(company, exchangeDate).data
			} ?: XXX.getExchangeWithCurrency(“RMB”, exchangeDate).data
			}

4、takeIf的使用总结

param?.takeIf{it.isBlank()}?.let{//it.isBlank()成立要做的事情}?:{
//it.isBlank()不成立要做的事情}

5、takeUnless的使用

param?.takeUnless{it.isBlank()}?.let{ //it.isBlank()不成立要做的事情}?:{//it.isBlank()成立要做的事情}