CODEWITHSUNDEEP
classscala
Pengfei Liu
Pengfei Liu

Reputation: 91

New a scala class with another class as param meet "type mismatch" error?

class base[T] () {
    def tell(t: T) { }
}

class test[T](a: T, b: base[T]){
    b.tell("sssssssssss")
}

val b = new base[String]()
val s:String = "12354555"
val t = new test[String](s, b)

I have two classes, one is class base, the other is test.
Class test has two params.

After run the code, I get such a type mismatch error.

error: type mismatch;
 found   : String("sssssssssss")
 required: T
    b.tell("sssssssssss")
               ^
one error found

In my code, already defined a type String b, but in class test the type of b is T.

Upvotes: 1

Views: 87

Answers (2)

bwroga
bwroga

Reputation: 5459

In the example you gave, T is a String, but it doesn't have to be. It could be anything.

You pass a String to b.tell() no matter what, but b.tell()'s argument type is not guaranteed to be a String.

Upvotes: 1

Yuriy
Yuriy

Reputation: 2769

At compilation moment type variable T in class test is not String, but you try to call it with String

Two possible solutions:

a) Set Lower bounds for paramter T

class test[T >: String](a: T, b: base[T]){
    b.tell("sssssssssss")
}

b) Or change type of prameter b:

class test[T](a: T, b: base[String]){
    b.tell("sssssssssss")
}

Upvotes: 4

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