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In Scala v 2.7.7
I have a file with
class Something[T] extends Other
object Something extends OtherConstructor[Something]
This throws the error:
class Something takes type parameters
object Something extends OtherConstructor[Something] {
However, I can't do this
object Something[T] extends OtherConstructor[Something[T]]
It throws an error:
error: ';' expected but '[' found.
Is it possible to send type parameters to object? Or should I change and simply use Otherconstructor
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you can access your Scala command-line arguments using the args array, which is made available to you implicitly when you extend App . As an example, your code will look like this: object Foo extends App { if (args. length == 0) { println("dude, i need at least one parameter") } val filename = args(0) ... }
=> is syntactic sugar for creating instances of functions. Recall that every function in scala is an instance of a class. For example, the type Int => String , is equivalent to the type Function1[Int,String] i.e. a function that takes an argument of type Int and returns a String .
A classOf[T] is a value of type Class[T] . In other words, classOf[T]: Class[T] . For example: scala> val strClass = classOf[String] strClass: Class[String] = class java. lang. String scala> :t strClass Class[String]
Language. Methods in Scala can be parameterized by type as well as by value. The syntax is similar to that of generic classes. Type parameters are enclosed in square brackets, while value parameters are enclosed in parentheses.
You could use:
object Something extends OtherConstructor[Something[_]]
You will of course be restricted by having an existential type with no upper bound in place instead of a concrete type. This solution may not make sense and you might need one object per concrete type T, for those T's which you care about, e.g.
object StringSomething extends OtherConstructor[Something[String]]
But then this has the (possible) disadvantage that StringSomething is not the companion object of Something.
However, my advice would be don't start messing about designing generic APIs (especially self-referential ones like the above) unless you really, really know what you are doing. It will almost certainly end in tears and there are plenty of CORE Java API's which are terrible because of the way generics have been added (the RowSorter API on JTable being one example)
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