从Kotlin中的“buildSequence”返回

只是使用 return@buildSequence ,这是一个 labeled return from lambda 返回 意思是“从函数中返回” foo '.

Whats does “return@” mean?

由于kotlinv1.3.x首选序列语法发生了变化。 ( buildSequence kotlin.sequences.sequence )

更新的“从生成器提前返回”代码段(包括 try-catch == null 早期返回示例)对于post 1.3.x Kotlin:

// gen@ is just a subjective name i gave to the code block.
// could be `anything@` you want
// Use of named returns prevents "'return' is not allowed here" errors.
private fun getItems() = sequence<Item> gen@ {

    val cursor: Cursor?
    try {
        cursor = contentResolver.query(uri,*args)
    } catch (e: SecurityException) {
        Log.w(APP_NAME, "Permission is not granted.")
        return@gen
    }

    if (cursor == null) {
        Log.w(APP_NAME, "Query returned nothing.")
        return@gen
    }

    // `.use` auto-closes Closeable. recommend.
    // https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.io/use.html 
    cursor.use {
        // iterate over cursor to step through the yielded records
        while (cursor.moveToNext()) {
            yield(Item.Factory.fromCursor(cursor))
        }
    }
}

(之前所有帮助我进入“命名返回”轨道的帖子,请点击Thx。)