How to use scala type alias (Int, String)

Question

In a situation similar to this

type abc=(Int,String)
val list=mutable.set[abc]()

How would I add something to the list? What does something with type (Int,String) look like? I tried doing things similar to list+=(5,"hello") but nothing I tried worked.

Answer 1

I find the existing answer distracting. It doesn't explain what the problem is, which is simply that the parenthesis are being interpreted as parameter parenthesis, not tuple parenthesis. Look here:

scala> list+=(5,"hello")
<console>:10: error: type mismatch;
 found   : Int(5)
 required: abc
    (which expands to)  (Int, String)
              list+=(5,"hello")
                     ^
<console>:10: error: type mismatch;
 found   : String("hello")
 required: abc
    (which expands to)  (Int, String)
              list+=(5,"hello")
                       ^

scala> list+=(5 -> "hello")
res1: list.type = Set((5,hello))

scala> list+=((5,"hello"))
res2: list.type = Set((5,hello))

The first time fails because you are calling the method += with two parameters, instead of calling it with one parameter that is a tuple.

The second time works because I used -> to denote the tuple.

The third time works because I put the extra tuple-parenthesis to denote the tuple.

That said, calling the Set a list is bad, because people would tend to think it is a List.

Answer 2

Not entirely sure what you are exactly looking for but here are some examples of adding a type of abc to a list which also includes the REPL output.

type abc = (Int, String)
defined type alias abc

scala> val item : abc = (1, "s")
item: (Int, String) = (1,s)

// i.e. Creating a new abc
scala> val item2 = new abc(1, "s")
item2: (Int, String) = (1,s)

scala> val list = List(item, item2)
list: List[(Int, String)] = List((1,s), (1,s))

// Shows an explicit use of type alias in declaration
val list2 = List[abc](item, item2)
list2: List[(Int, String)] = List((1,s), (1,s))

// Adding to a mutable list although immutable would be a better approach
scala> var list3 = List[abc]()
list3: List[(Int, String)] = List()

scala> list3 = (5, "hello") :: list3
list3: List[(Int, String)] = List((5,hello))

// Appending abc (tuple) type to mutable list
scala> list3 = list3 :+ (5, "hello")
list3: List[(Int, String)] = List((5,hello), (5,hello))