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    <h2>Alternatives</h2> <p>Use <code>null</code> as a last resort. As already mentioned, <code>Option</code> replaces most usages of null. If you using <code>null</code> to implement deferred initialisation of a field with some expensive calculation, you should use a <code>lazy val</code>.</p> <h2>Canonical initialisation to null</h2> <p>That said, Scala does support <code>null</code>. I personally use it in combination with Spring Dependency Injection.</p> <p>Your code is perfectly valid. However, I suggest that you use <code>var t: T = _</code> to initialize <code>t</code> to it's default value. If <code>T</code> is a primitive, you get the default specific to the type. Otherwise you get <code>null</code>.</p> <p>Not only is this more concise, but it is necessary when you don't know in advance what <code>T</code> will be:</p> <pre><code>scala&gt; class A[T] { var t: T = _ } defined class A scala&gt; new A[String].t res0: String = null scala&gt; new A[Object].t res1: java.lang.Object = null scala&gt; new A[Int].t res2: Int = 0 scala&gt; new A[Byte].t res3: Byte = 0 scala&gt; new A[Boolean].t res4: Boolean = false scala&gt; new A[Any].t res5: Any = null </code></pre> <h2>Advanced</h2> <p>Using <code>var t: T= null</code> is a compile error if T is unbounded:</p> <pre><code>scala&gt; class A[T] { var t: T = null } &lt;console&gt;:5: error: type mismatch; found : Null(null) required: T class A[T] { var t: T = null } </code></pre> <p>You can add an implicit parameter as evidence that <code>T</code> is nullable -- a subtype of <code>AnyRef</code> not a subtype of <code>NotNull</code> This isn't fully <a href="https://stackoverflow.com/questions/2335496/how-does-the-notnull-trait-work-in-2-8-and-does-anyone-actually-use-it">baked</a>, even in Scala 2.8, so just consider it a curiousity for now. </p> <pre><code>scala&gt; class A[T](implicit ev: Null &lt;:&lt; T) { var t: T = null } defined class A </code></pre>
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    1. POIs this the proper way to initialize null references in Scala?
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    1. POIs this the proper way to initialize null references in Scala?
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    1. COWhat's that <:< thing there?
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      1. USDimitris Andreou
    2. COVery helpful! But why does it NOT suffice to put an upper bound of AnyRef on T, i.e. `class A[ T <: AnyRef ] { var t:T = null }` ?
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    3. COScala has an experimental trait, `NotNull`. If we have `class C extends NotNull`, `null` is not a subtype of `C`. This feature was turned off by default in Scala 2.8, as it isn't fully baked. But it is still around enough to mean you have to write `class A[T >: Null] { var t: T = null }` rather than `class A[T <: AnyRef] { var t: T = null }`
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