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POWeird initialisation when override val met DelayedInit in Scala
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  1. POWeird initialisation when override val met DelayedInit in Scala
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    copied!<p>Following code's output makes me confused.</p> <h2>code</h2> <pre><code>object Test1 { trait A { val s: String = "A" println(s"s = $s") } abstract class B extends A with DelayedInit { override def delayedInit(body: =&gt; Unit) = { println("B " + "1" * 80) body println("B " + "2" * 80) } } abstract class C extends A with DelayedInit { override val s: String = "C" override def delayedInit(body: =&gt; Unit) = { println("C " + "1" * 80) body println("C " + "2" * 80) } } def main { println("-- new B begin") new B { println("new B context") } println("-- new B end") println("-- new C begin") new C { println("new C context") } println("-- new C end") } } object Test2 { trait A { def s: String = "A" println(s"s = $s") } abstract class B extends A with DelayedInit { override def delayedInit(body: =&gt; Unit) = { println("B " + "1" * 80) body println("B " + "2" * 80) } } abstract class C extends A with DelayedInit { override def s: String = "C" override def delayedInit(body: =&gt; Unit) = { println("C " + "1" * 80) body println("C " + "2" * 80) } } def main { println("-- new B begin") new B { println("new B context") } println("-- new B end") println("-- new C begin") new C { println("new C context") } println("-- new C end") } } println("Test1") Test1.main println("Test2") Test2.main </code></pre> <h2>output</h2> <pre><code>Test1 -- new B begin s = A B 11111111111111111111111111111111111111111111111111111111111111111111111111111111 new B context B 22222222222222222222222222222222222222222222222222222222222222222222222222222222 -- new B end -- new C begin s = null C 11111111111111111111111111111111111111111111111111111111111111111111111111111111 C 22222222222222222222222222222222222222222222222222222222222222222222222222222222 C 11111111111111111111111111111111111111111111111111111111111111111111111111111111 new C context C 22222222222222222222222222222222222222222222222222222222222222222222222222222222 -- new C end Test2 -- new B begin s = A B 11111111111111111111111111111111111111111111111111111111111111111111111111111111 new B context B 22222222222222222222222222222222222222222222222222222222222222222222222222222222 -- new B end -- new C begin s = C C 11111111111111111111111111111111111111111111111111111111111111111111111111111111 new C context C 22222222222222222222222222222222222222222222222222222222222222222222222222222222 -- new C end </code></pre> <p>Tried both scala 2.10.2 &amp; 2.11.0-M3.</p> <p>In my understanding, Test1 should be the same as Test2. Here is two questions:</p> <ul> <li>Why DelayedInit has been called twice in Test1.C? There is not other class inherits the trait in the class hierarchy</li> <li>Why <code>s == null</code> in Test1.C?</li> </ul>
 

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