CODEWITHSUNDEEP
scala
Ian Phillips
Ian Phillips

Reputation: 567

Why does this not type check?

Why does the following code fail to type check:

var a = Map.empty[String, Integer]
var b: Integer = a.getOrElse("", 0)
b += 1
b = b + 1
val c: Integer = a.getOrElse("", 0) + 1

The first four lines are fine but the last line fails with “Type mismatch: expected String actual Int”. Surely this is doing the same thing as lines 2 & 4 combined?

Upvotes: 1

Views: 125

Answers (1)

Ben Reich
Ben Reich

Reputation: 16324

Try using Int instead of Integer:

var a = Map.empty[String, Int]
var b: Int = a.getOrElse("", 0)
b += 1
b = b + 1
val c: Int = a.getOrElse("", 0) + 1

Int and Integer are not the same type in Scala. From this post:

Integer is just an alias for java.lang.Integer. Int is the Scala integer with the extra capabilities.

So what's happening is that when you do a.getOrElse("", 0), the return type is the common super type of Integer and Int, which is Any. Then you try to add to anAny`, which doesn't work!

Upvotes: 4

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