Is there a difference in scala type bound notation direction?

Question

Is there a difference in scala type bound notation direction, as in is [B <: A] the same as [A >: B]?

score 2 · Accepted Answer · answered Aug 07 '15 at 14:57

2

B <: A means that B has an upper-bound of A. Which means that B can be any type from Nothing to A in the type hierarchy.

A >: B means that A has a lower-bound of B, which means that A can be anything from B to Any in the type hierarchy.

In general, they do not mean the same thing. Each one imposes a bound on a different type parameter. This isn't variance notation either, these are type bounds.

answered Aug 07 '15 at 14:57

Michael Zajac

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Like `super` vs `extends` in Java iirc when dealing with type signatures. – Carcigenicate Aug 07 '15 at 15:01

score 0 · Answer 2 · answered Aug 07 '15 at 14:55

0

Here [B <: A] you declare type B which extends A, here [A >: B] you declare type A which is a parent of type B.

answered Aug 07 '15 at 14:55

ka4eli

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Is there a difference in scala type bound notation direction?

2 Answers2