Scala: Difference between revisions
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A trait with a self type cannot be used without mixed in that trait first. | A trait with a self type cannot be used without mixed in that trait first. | ||
< | |||
<syntaxhighlight lang="scala"> | |||
trait User { | trait User { | ||
def username: String | def username: String | ||
| Line 17: | Line 18: | ||
def tweet(tweetText: String) = println(s"$username: $tweetText") | def tweet(tweetText: String) = println(s"$username: $tweetText") | ||
} | } | ||
</ | </syntaxhighlight> | ||
A question is how it is different from trait subclasses. | A question is how it is different from trait subclasses. | ||
See [https://docs.scala-lang.org/tour/self-types.html Official tour], [http://jonasboner.com/real-world-scala-dependency-injection-di/ a discussion on the cake pattern] and [https://stackoverflow.com/questions/1990948/what-is-the-difference-between-self-types-and-trait-subclasses a StackOverflow question] about this. | See [https://docs.scala-lang.org/tour/self-types.html Official tour], [http://jonasboner.com/real-world-scala-dependency-injection-di/ a discussion on the cake pattern] and [https://stackoverflow.com/questions/1990948/what-is-the-difference-between-self-types-and-trait-subclasses a StackOverflow question] about this. | ||
Revision as of 23:27, 26 May 2020
Type bounds
B <: U imposes a upper bound on type U, while B >: L imposes a lower bound. This is useful for generic methods that takes only classes on a particular inheritance tree as its type parameters.
The official tour has a pretty good explanation: Upper bounds and Lower bounds
Self Type
A trait with a self type cannot be used without mixed in that trait first.
trait User {
def username: String
}
trait Tweeter {
this: User => // reassign this
def tweet(tweetText: String) = println(s"$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.