CODEWITHSUNDEEP
scala
xlgforever
xlgforever

Reputation: 23

what does more than one Parameterized Types mean?

I'm learning some Scala example from somewhere, it looks like as below:

class className[T <: classTypeA : classTypeB](some args)....

Or:

class className[T<:classTypeA with trait1](some args)...

Some tutorial explain that T <: classTypeA means T must be the subclass of classTypeA. I don't understand why there are two types after <:, and what with trait1 means?

Upvotes: 0

Views: 56

Answers (1)

Tim
Tim

Reputation: 27356

class className[T <: classTypeA : classTypeB](some args)

In this declaration classTypeB is a type class and this is equivalent to

class className[T <: classTypeA](some args)(implicit ev: classTypeB[T])

There must be a suitable instance of classTypeB[T] in scope for this to compile. This allows fine-grain control of which types are accepted as parameters to the class.

class className[T <: classTypeA with trait1](some args)

This declaration says that T must be a subclass of the type classTypeA with trait1.

Upvotes: 2

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