CODEWITHSUNDEEP
scalascala-collections
ps0604
ps0604

Reputation: 1071

Appending to Seq in Scala does not compile

In this code I'm trying to add values to a Seq[Seq[String]] structure, but the line shown below throws a compilation error, why is that?

var values2 = Seq[Seq[String]]()
values2 = values2 :+ Seq[String]()
for ( x <- 0 to 5) {
      values2(0) = values2(0) :+ (x + "")  // <-- value update is not a member of Seq[Seq[String]]
    }

Upvotes: 2

Views: 284

Answers (2)

Peter Fitch
Peter Fitch

Reputation: 253

import scala.collection.mutable

var values2 = mutable.Seq[mutable.Seq[String]]()
values2 = values2 :+ mutable.Seq[String]()
for (x <- 0 to 5) {
  values2(0) = values2(0) :+ (x + "")
}

You can solve this by explicitly using mutable.Seq instead of the default Seq, which is immutable.

Upvotes: 1

Yevhenii Popadiuk
Yevhenii Popadiuk

Reputation: 1054

That's happens because inner collection is immutable and you can't reassign it's value with =.

But you can use update method of it (similar to copy method on case-classes), so it'll be like this:

for ( x <- 0 to 5) {
  values2 = values2.updated(0, values2(0) :+ (x + ""))
}

Now you just coping values2 collection with one element changed.

Upvotes: 3

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