kotlin 中的takeif和takeunless的使用

ゝ一纸荒年。 2022-10-04 15:00 163阅读 0赞

## 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\}