Kotlin_takeif.md

takeif

源码实现

public inline fun <T> T.takeIf(predicate: (T) -> Boolean): T? 
    = if (predicate(this)) this else null

---

使用方法一

// Original Code
if (status) { doThis() }

// Modified Code
takeIf { status }?.apply { doThis() }

---

使用方法二

// Original code
if (someObject != null && status) {
   doThis()
}

// Improved code
someObject?.takeIf{ status }?.apply{ doThis() }

---

使用方法三

// Original code
if (someObject != null && someObject.status) {
   doThis()
}
// Better code
if (someObject?.status == true) {
   doThis()
}
// Improved code
someObject?.takeIf{ it.status }?.apply{ doThis() }

使用方法四

val index 
   = input.indexOf(keyword).takeIf { it >= 0 } ?: error("Error")
val outFile 
   = File(outputDir.path).takeIf { it.exists() } ?: return false	

注意事项

//doThis() 方法一定会执行而无论 status 是 true 还是 false
// Syntactically still correct. But logically wrong!!
someObject?.takeIf{ status }.apply{ doThis() }

//doThis() 方法不一定会执行，会判断status是否为空，是否为true
// The correct one (notice the nullability check ?)
someObject?.takeIf{ status }?.apply{ doThis() }