CODEWITHSUNDEEP
javascala
TheReturningVoid
TheReturningVoid

Reputation: 111

Strange type mismatch in Scala

I'm trying to invoke a constructor that takes a varargs in Scala. The constructor is written in a Java class and takes two parameters, a Block and IBlockState.... The following code doesn't seem to compile, however:

new BlockStateList(this, Seq[IBlockState[_ <: Comparable[_]]](FACING, DAMAGE):_*)

The compiler reports with this message:

Error:(58, 66) type mismatch;
 found   : Seq[net.minecraft.server.v1_8_R3.IBlockState[_ <: Comparable[_]]]
 required: Seq[net.minecraft.server.v1_8_R3.IBlockState[? <: Comparable[?0]] forSome { type ?0 <: Comparable[?0] }]
   new BlockStateList(this, Seq[IBlockState[_ <: Comparable[_]]](FACING, DAMAGE):_*)
                                      ^

The required type doesn't seem syntactically correct to me, and I have no idea as to what it wants me to provide.

All help is greatly appreciated!

Upvotes: 0

Views: 159

Answers (1)

ayvango
ayvango

Reputation: 5977

The problem is not related to varargs, but to the content of the sequence.

As I have deduced Comparable is restricted to its type parameter. Something like

trait Comparable[C <: Comparable[C]]

See more info about this pattern. So to denote this type requirement you need advanced existential types specification. MyType[_] is shortcut to full MyType[A] forSome {type A}. In your case compiler expects

Seq[IBlockState[_ <: Comparable[C]] forSome { type C <: Comparable[C] }]()

instead of 

Seq[IBlockState[_ <: Comparable[_]]]()

Upvotes: 2

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