Scala 中的“def"与“val"与“lazy val"评估 [英] `def` vs `val` vs `lazy val` evaluation in Scala

问题描述

我的理解是否正确

• def 每次被访问时都会被评估

• def is evaluated every time it gets accessed

lazy val 一旦被访问就会被评估

lazy val is evaluated once it gets accessed

val 一旦进入执行范围就被评估?

val is evaluated once it gets into the execution scope?

推荐答案

是的，虽然对于第三个我会说当那个语句被执行时"，因为，例如:

Yes, though for the 3rd one I would say "when that statement is executed", because, for example:

def foo() {
    new {
        val a: Any = sys.error("b is " + b)
        val b: Any = sys.error("a is " + a)
    }
}

这给出了 b 为空".b 永远不会被评估并且它的错误永远不会被抛出.但是一旦控制进入块，它就在范围内.

This gives "b is null". b is never evaluated and its error is never thrown. But it is in scope as soon as control enters the block.

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