英文:
Kotlin get value by key from map
问题
假设我们有一个映射：
val charToCount = mapOf('a', 3)
任务是通过相应的键检索值 3。问题在于 map.get(...) 返回可空类型 T? 而不是 T。如果保证键在映射中存在且相应的值 != null，怎样才是将该值转换为非空类型的最佳实践呢？
从我的理解来看，有两种方法：
val count = charToCount['a']!!val count = charToCount['a'] ?: error("...")
但是这两种方法都不够简洁。是否有更好的方法来处理可空类型呢？
英文:
Let's assume we have a map:
val charToCount = mapOf('a', 3)
The task is to retrieve the value 3 by the corresponding key. The problem is map.get(...) returns nullable type T? instead of T. What's the best practice to convert the value to non-nullable type if there is a guarantee that the key is present in the map and the corresponding value != null?
Off the top of my head there are two ways:
val count = charToCount['a']!!val count = charToCount['a'] ?: error("...")
But both of them don't seem concise. Are there any better approaches to chip away with a nullable type?
答案1
得分: 6
适当的方法是：
val count: Int = charToCount.getValue('a')
这会根据文档“在映射中没有这样的键时抛出异常”。
如果你希望更加简洁，抱歉可能不能比得上 !!。
英文:
The appropriate method is
val count: Int = charToCount.getValue('a')
...which "throws an exception if there is no such key in the map," according to its docs.
Sorry if you were hoping for something more concise; if you want something short, you can't possibly beat !!.
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