Scala“<-"表示理解 [英] Scala "<-" for comprehension
问题描述
我发现Scala总是对任何事物都有自然的解释".总是像哦，但这只是在带有该参数的那个对象上调用的函数".从某种意义上说，没有什么是我们从其他语言中了解到的真正的编译器魔术.
I have found that Scala always has a "natural explanation" to anything. Always something like "ohh, but that's just a function being called on this and that object with this and that parameter". In a sense, nothing is really compiler-magic as we know it from other languages.
我的问题是在以下代码中使用的 <- 运算符:
My question is on the <- operator as used in the following code:
for(i <- 0 to 10) println(i)
在此示例中，我可以看到它被重写为类似以下内容:
In this example I can see it being rewritten to something like:
0.to(10).foreach((i:Int)=>println(i))
但这不能解释 i 是如何被带入foreach函数内部的匿名函数的.在编写 i 时，它不是对象，也不是声明的变量.那么，它是什么，以及它如何被延续到foreach的内部?
but this doesn't explain how the i got carried into the anonymous function inside the foreach function. At the point where you write i it is not an object, and not yet a declared variable. So what is it, and how is it being carried over to the inside of foreach?
我的猜测是，我终于发现了一些实际上是编译器魔术
My guess is that I finally discovered something which is in fact compiler magic
感谢您的时间.
为了澄清，我的问题是:<-运算符如何在代码的第一行中工作，因为我不是可在其上调用它的函数的对象.
To clarify, my question is: how does the <- operator work in the 1st line of code since i is not an object on which it can be called as a function.
推荐答案
<-是语言定义的关键字符号，=>也是，但与->(已定义的符号)形成鲜明对比.由于它是Scala基本语法的一部分，因此可以用来创建绑定(对于您的示例中的i而言)，这是用户定义的构造无法完成的.
<- is a language-defined keyword symbol, as is => but in distinct contrast to -> (which is a defined symbol). Because it is part of the basic Scala grammar, it can be used to create bindings (for the i in your example) which is something that cannot be done by user-defined constructs.
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