Scala Map：神秘的语法糖？
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Scala Map: mysterious syntactic sugar?
提问by oxbow_lakes
I have just found out this syntax for a scala Map(used here in mutableform)
我刚刚发现了 Scala 的这种语法Map（此处以可变形式使用）
val m = scala.collection.mutable.Map[String, Int]()
m("Hello") = 5
println(m) //PRINTS Map(Hello -> 5)
Now I'm not sure whether this is syntactic sugarbuilt in to the language, or whether something more fundamental is going on here involving the fact that a map extends a PartialFunction. Could anyone explain?
现在我不确定这是否是语言内置的语法糖，或者这里是否发生了一些更基本的事情，涉及映射扩展了PartialFunction. 谁能解释一下？
回答by starblue
If you mean (it would be nice if you could be more explicit)
如果你的意思是（如果你能更明确一点就好了）
m("Hello") = 5
that is intended syntactic sugar for
那是为了语法糖
m.update("Hello", 5)
independent of what m is. This is analogous to
与 m 是什么无关。这类似于
m("Hello")
which is syntactic sugar for
这是语法糖
m.apply("Hello")
(I'm just reading "Programming in Scala".)
（我只是在读“在 Scala 中编程”。）
回答by Daniel Spiewak
@starblue is correct. Note that you can also do rather creative things with updatesuch as returning values otherthan what was assigned. For example:
@starblue 是正确的。请注意，您也可以对颇具创意的东西update比如返回值等比分配。例如：
val a = Map(1 -> "one") // an immutable Map[Int, String]
val b = a(2) = "two"
val c = b(5) = "five"
val d = c(1) = "uno"
d == Map(1 -> "uno", 2 -> "two", 5 -> "five") // => true
This works because immutable.Map#updatereturns an instance of the new Map. It looks a little odd to the C-trained eye, but you get used to it.
这是有效的，因为immutable.Map#update返回了 new 的一个实例Map。对于受过 C 培训的人来说，这看起来有点奇怪，但你已经习惯了。
