Different behaviour of case match pattern for strings

Question

I am trying to use strings in a case class like java switch-case statements switch(someString). But scala match statement always resolves to the first block.

whichTopic match {
  case accounts ⇒ {
    logger.info("!!!! ---- FOR ACCOUNTS --- !!! ")

  }
  case users ⇒ {
    logger.info("!!!! ---- FOR USERS --- !!! ")
    // TODO : Handle errors from the consumer
  }
}

Even when whichTopic value has users, it goes into the accounts block

case x => will match all input because x is an unbound variable that can hold any value being matched against. case accounts => is the same. You're creating a variable named accounts that can hold (and thus match) any value. — jwvh
– jwvh, Commented Jul 10, 2019 at 5:22
ahh...so i was never using the variable to identify which block it has to go to. Thanks for explaining. — ForeverLearner
– ForeverLearner, Commented Jul 10, 2019 at 5:30

Xavier Guihot · Accepted Answer · 2019-07-10 07:11:52Z

3

It's because you didn't use it correctly - what you actually did is 2 cases of "alias" the whichTopic variable to accounts or users variables, but didn't specify what is "special" about them.

You should do something like:

whichTopic match {
  case accounts if accounts.startsWith("accounts") => logger.info("!!!! ---- FOR ACCOUNTS --- !!! ")
  case users if users.startsWith("users") => logger.info("!!!! ---- FOR USERS --- !!! ")
}

This is a case to check if is the strings start with accounts or users.

Of course, you can replace startsWith with any string method you want - like contains or something else which suits your case.

edited Jul 10, 2019 at 7:11

Xavier Guihot

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answered Jul 10, 2019 at 5:17

Gal Naor

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Comments

Alexey Romanov · Accepted Answer · 2019-07-10 05:34:43Z

3

ahh...so i was never using the variable to identify which block it has to go to.

If you want to check equality to an existing variable, you can write

case x if x == accounts => ...

(as in Gal Naor's answer) or

case `accounts` => ...

answered Jul 10, 2019 at 5:34

Alexey Romanov

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