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  1. PO
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    <p>This is interesting! If you put the class definitions into a file and compile it using <code>scalac -print test.scala</code> you will see something like this,</p> <pre><code>[[syntax trees at end of cleanup]] // scala package &lt;empty&gt; { class A extends Object { def g(): String = A.f(); def &lt;init&gt;(): A = { A.super.&lt;init&gt;(); () } }; object A extends Object { private[this] val f: String = _; &lt;stable&gt; &lt;accessor&gt; def f(): String = A.this.f; def &lt;init&gt;(): A.type = { A.super.&lt;init&gt;(); A.this.f = "Object A"; () } }; class B extends A { &lt;synthetic&gt; private[this] val x$1: runtime.BoxedUnit = _; def &lt;init&gt;(): B = { B.super.&lt;init&gt;(); B.this.x$1 = { case &lt;synthetic&gt; val x1: String = ("Object B": String("Object B")); case5(){ if (A.f().==(x1)) { val x2: String = x1; matchEnd4(scala.runtime.BoxedUnit.UNIT) } else case6() }; case6(){ matchEnd4(throw new MatchError(x1)) }; matchEnd4(x: runtime.BoxedUnit){ scala.runtime.BoxedUnit.UNIT } }; () } } } </code></pre> <p>This shows that the compiler creates a class <code>B</code> with an initialization that performs a match checking to see that the value you used in override the <code>val A.f</code> is equal to the original value <code>if (A.f().==(x1))</code>. Doesn't seem to be too useful right? If they're not equal it throws the match error by calling <code>case6()</code>. We can confirm this by changing the definition of the <code>class B</code> to <code>override val A.f = "Object A"</code>.</p> <pre><code>class B extends A { override val A.f = "Object A" } scala&gt; val b = new B b: B = B@1fc6dc6 </code></pre> <p>So how to fix it? You can just do this,</p> <pre><code>class B extends A { override def g = "Object B" } scala&gt; val b = new B b: B = B@19bdb65 scala&gt; b.g res1: String = Object B </code></pre> <p>or</p> <pre><code>class B extends A { val f = "Object B" } scala&gt; val b = new B b: B = B@1e5ed7b scala&gt; b.f res0: String = Object B </code></pre>
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    1. POOverriding Companion Object Values and Scala MatchError
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    1. UStysonjh
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      1. VTUpMod
    1. COYou may consider using traits: http://stackoverflow.com/a/7625150/1274818
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    2. COYour fixes are a smart way to get around this simple code example, but not what I am really looking for, since I want to call the original A.f method.
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      1. USdeepkimo
    3. COYes, traits are a good way to structure this, but in my case I want to test code that already exists without changing the main code.
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