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    copied!<pre><code>1. def bar[A &lt;: java.io.Serializable](i:A) = i </code></pre> <p>&lt;: - guarantees that instance of <strong>i</strong> of type parameter <strong>A</strong> will be subtype of <strong>Serializable</strong></p> <pre><code>2. def foo[A](i:A)(implicit ev : A &lt;:&lt; java.io.Serializable) = i </code></pre> <p>&lt;:&lt; - guarantees that execution context will contains implicit value (for <strong>ev</strong> paramenter) of type <strong>A</strong> what is subtype of <strong>Serializable</strong>. This implicit defined in Predef.scala and for <strong><em>foo</em></strong> method and it is prove if instance of type parameter A is subtype of <strong>Serializable</strong>: </p> <pre><code>implicit def conforms[A]: A &lt;:&lt; A = singleton_&lt;:&lt;.asInstanceOf[A &lt;:&lt; A] </code></pre> <p>fictional case of using &lt;:&lt; operator:</p> <pre><code>class Boo[A](x: A) { def get: A = x def div(implicit ev : A &lt;:&lt; Double) = x / 2 def inc(implicit ev : A &lt;:&lt; Int) = x + 1 } val a = new Boo("hi") a.get // - OK a.div // - compile time error String not subtype of Double a.inc // - compile tile error String not subtype of Int val b = new Boo(10.0) b.get // - OK b.div // - OK b.inc // - compile time error Double not subtype of Int val c = new Boo(10) c.get // - OK c.div // - compile time error Int not subtype of Double c.inc // - OK </code></pre> <ul> <li>if we not call methods what not conform &lt;:&lt; condition than all compile and execute.</li> </ul>
 

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