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Hoppinglife (talk | contribs) Created page with "=== Type bounds === <code>B <: U</code> imposes a ''upper bound'' on type <code>U</code>, while <code>B >: L</code> imposes a ''lower bound''. This is useful for generic meth..." |
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The official tour has a pretty good explanation: [https://docs.scala-lang.org/tour/upper-type-bounds.html Upper bounds] and [https://docs.scala-lang.org/tour/lower-type-bounds.html Lower bounds] | The official tour has a pretty good explanation: [https://docs.scala-lang.org/tour/upper-type-bounds.html Upper bounds] and [https://docs.scala-lang.org/tour/lower-type-bounds.html Lower bounds] | ||
=== Self Type === | |||
A trait with a self type cannot be used without mixed in that trait first. | |||
<pre class="hljs scala"> | |||
trait User { | |||
def username: String | |||
} | |||
trait Tweeter { | |||
this: User => // reassign this | |||
def tweet(tweetText: String) = println(s"$username: $tweetText") | |||
} | |||
</pre> | |||
A question is how it is different from trait subclasses. | |||
See [https://docs.scala-lang.org/tour/self-types.html Official tour], [http://jonasboner.com/real-world-scala-dependency-injection-di/ a discussion on the cake pattern] and [https://stackoverflow.com/questions/1990948/what-is-the-difference-between-self-types-and-trait-subclasses a StackOverflow question] about this. | |||
Revision as of 22:58, 26 May 2020
Type bounds
B <: U imposes a upper bound on type U, while B >: L imposes a lower bound. This is useful for generic methods that takes only classes on a particular inheritance tree as its type parameters.
The official tour has a pretty good explanation: Upper bounds and Lower bounds
Self Type
A trait with a self type cannot be used without mixed in that trait first.
trait User {
def username: String
}
trait Tweeter {
this: User => // reassign this
def tweet(tweetText: String) = println(s"$username: $tweetText")
}
A question is how it is different from trait subclasses.
See Official tour, a discussion on the cake pattern and a StackOverflow question about this.