scala - Why is foreach better than get for Scala Options?

Question

Why using foreach, map, flatMap etc. are considered better than using get for Scala Options? If I useisEmpty I can call get safely.

Answer 1

Well, it kind of comes back to "tell, don't ask". Consider these two lines:

if (opt.isDefined) println(opt.get)
// versus
opt foreach println

In the first case, you are looking inside opt and then reacting depending on what you see. In the second case you are just telling opt what you want done, and let it deal with it.

The first case knows too much about Option, replicates logic internal to it, is fragile and prone to errors (it can result in run-time errors, instead of compile-time errors, if written incorrectly).

Add to that, it is not composable. If you have three options, a single for comprehension takes care of them:

for {
  op1 <- opt1
  op2 <- opt2
  op3 <- opt3
} println(op1+op2+op3)

With if, things start to get messy fast.

Answer 2

One nice reason to use foreach is parsing something with nested options. If you have something like

val nestedOption = Some(Some(Some(1)))
for {
  opt1 <- nestedOption
  opt2 <- opt1
  opt3 <- opt2
} println(opt3)

The console prints 1. If you extend this to a case where you have a class that optionally stores a reference to something, which in turn stores another reference, for comprehensions allow you to avoid a giant "pyramid" of None/Some checking.

Answer 3

There are already excellent answers to the actual question, but for more Option-foo you should definitely check out Tony Morris' Option Cheat Sheet.

Answer 4

関数を使用して実行する代わりに、、、などをmap直接適用する方が便利な理由は、関数がどちらかで機能し、値が存在することを確認するために特別なチェックを行う必要がないためです。foreachflatMapOptiongetSome None

val x: Option[Int] = foo()
val y = x.map(_+1) // works fine for None
val z = x.get + 1  // doesn't work if x is None

yここでの結果はです。これは、オプションの場合、同様に未定である可能性があるOption[Int]ため、望ましいものです。は機能しないため、エラーが発生しないようにするために、多くの追加作業を行う必要があります。によって行われる追加の作業。xygetNonemap

Answer 5

Put simply:

• If you need to do something (a procedure when you don't need to capture the return value of each invocation) only if the option is defined (i.e. is a Some): use foreach (if you care about the results of each invocation, use map)

• If you need to do something if the option defined and something else if it's not: use isDefined in an if statement

• If you need the value if the option is a Some, or a default value if it is a None: use getOrElse

Answer 6

Trying to perform our Operations with get is more imperative style where u need to tel what to do and how to do . In other words , we are dictating things and digging more into the Options internals. Where as map,flatmap are more functional way of doing things where we are say what to do but not how to do.