【转】Scala: Example use for early definition / early initializer / pre-initialized fields

原文链接 http://stackoverflow.com/questions/16348541/scala-example-use-for-early-definition-early-initializer-pre-initialized-fi#

Let's see a example from the Programming in Scala book (page 451). If we have a definition like this:

trait RationalTrait { val numerArg: Int val denomArg: Int }

Then numerArg and denomArg are called abstract vals & the trait can be used directly without extends, like this:

val x = new RationalTrait { val numerArg = 1 val denomArg = 2 }

val y = new { val numerArg = 1 val denomArg = 1 } with RationalTrait

The above two are both valid Pre-initializing of abstract val in trait, except that when you need to put an expression value to abstract vals, you can only use the later form, like this:

val z = new { val numerArg = 1 * x val denomArg = 2 * x } with RationalTrait

Another interesting example in book is to Pre-initialized fields in a class definition.

class RationalClass(n: Int, d: Int) extends { val numerArg = n val denomArg = d } with RationalTrait { def + (that: RationalClass) = new RationalClass( numer * that.denom + that.numer * denom, denom * that.denom ) }

转载于:https://www.cnblogs.com/ihongyan/p/4712298.html

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【转】Scala: Example use for early definition / early initializer / pre-initialized fields

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