Scala：for循环中的条件卫士

Question

I need some enlightenment about the guard in a for loop in Scala: my code is

for {
  enterprise <- itr
  preferName <- enterprise \* qpreferedName
  variantName <- enterprise \* qvariantName
  attrVRes <- enterprise \* qtype \@ attrRes
  if (text(preferName).contains(keyword) || text(variantName).contains(keyword))
} {
//loop code
}

Now it works file. But I want to check the value of keyword , if it's an empty string, I will not apply this guard ( if (text(preferName).contains(keyword) || text(variantName).contains(keyword)) ), otherwise apply it.

Can someone tell me a decent way to do it?

Answer 1

Since it seems that keyword is defined outside of the for comprehension, I would set up a boolean out there, then add it into the guard. Eg:

val keywordInvalid = keyword.isEmpty // Or however you want to define your condition

for {
  enterprise <- itr
  preferName <- enterprise \* qpreferedName
  variantName <- enterprise \* qvariantName
  attrVRes <- enterprise \* qtype \@ attrRes
  if keywordInvalid || text(preferName).contains(keyword) || text(variantName).contains(keyword)
} {
  //loop code
}

Or flip it (as per @Łukasz's comment):

val keywordValid = keyword.nonEmpty 
...
for {
  ...
  if keywordValid && ((text(preferName).contains(keyword) || text(variantName).contains(keyword))
} {
  //loop code
}

Answer 2

You can define such utility

def textContains(str: String): String => Boolean = str match {
  case "" => Function.const(true)
  case _ => text(_).contains(str)
}

and use it as

for {
 /* ... */
if Seq(preferName,variantName).exists(textContains(keyword))
} yield ???