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    <p>Scala has a restriction on automatic conversions to add a method, which is that it won't apply more than one conversion in trying to find methods. For example:</p> <pre><code>class A(val n: Int) class B(val m: Int, val n: Int) class C(val m: Int, val n: Int, val o: Int) { def total = m + n + o } // This demonstrates implicit conversion chaining restrictions object T1 { // to make it easy to test on REPL implicit def toA(n: Int): A = new A(n) implicit def aToB(a: A): B = new B(a.n, a.n) implicit def bToC(b: B): C = new C(b.m, b.n, b.m + b.n) // won't work println(5.total) println(new A(5).total) // works println(new B(5, 5).total) println(new C(5, 5, 10).total) } </code></pre> <p><strong>EDIT: View bounds ('&lt;%') are deprecated since Scala 2.11 <a href="https://issues.scala-lang.org/browse/SI-7629" rel="noreferrer">https://issues.scala-lang.org/browse/SI-7629</a></strong> (You can use type classes instead)</p> <p>However, if an implicit definition requires an implicit parameter itself(View bound), Scala <em>will</em> look for additional implicit values for as long as needed. Continue from the last example:</p> <pre><code>// def m[A &lt;% B](m: A) is the same thing as // def m[A](m: A)(implicit ev: A =&gt; B) object T2 { implicit def toA(n: Int): A = new A(n) implicit def aToB[A1 &lt;% A](a: A1): B = new B(a.n, a.n) implicit def bToC[B1 &lt;% B](b: B1): C = new C(b.m, b.n, b.m + b.n) // works println(5.total) println(new A(5).total) println(new B(5, 5).total) println(new C(5, 5, 10).total) } </code></pre> <p>"Magic!", you might say. Not so. Here is how the compiler would translate each one:</p> <pre><code>object T1Translated { implicit def toA(n: Int): A = new A(n) implicit def aToB(a: A): B = new B(a.n, a.n) implicit def bToC(b: B): C = new C(b.m, b.n, b.m + b.n) // Scala won't do this println(bToC(aToB(toA(5))).total) println(bToC(aToB(new A(5))).total) // Just this println(bToC(new B(5, 5)).total) // No implicits required println(new C(5, 5, 10).total) } object T2Translated { implicit def toA(n: Int): A = new A(n) implicit def aToB[A1 &lt;% A](a: A1): B = new B(a.n, a.n) implicit def bToC[B1 &lt;% B](b: B1): C = new C(b.m, b.n, b.m + b.n) // Scala does this println(bToC(5)(x =&gt; aToB(x)(y =&gt; toA(y))).total) println(bToC(new A(5))(x =&gt; aToB(x)(identity)).total) println(bToC(new B(5, 5))(identity).total) // no implicits required println(new C(5, 5, 10).total) } </code></pre> <p>So, while <code>bToC</code> is being used as an implicit conversion, <code>aToB</code> and <code>toA</code> are being passed as <em>implicit parameters</em>, instead of being chained as implicit conversions.</p> <p><strong>EDIT</strong></p> <p>Related question of interest:</p> <ul> <li><a href="https://stackoverflow.com/q/5598085/53013">A discussion on types, origin and precedence of implicits</a></li> </ul>
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    1. POHow can I chain implicits in Scala?
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    1. USDaniel C. Sobral
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    1. CONice explanation. The stated reason for disallowing implicit conversion chaining is to avoid complexity and debugging nightmare. I wonder why is then chaining allowed for implicit parameters?
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    2. CONice! I learned something new. This should be on the "hidden features" page.
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    3. COThanks! One minor issue: I had to add add explicit result types to the functions `aToB` and `bToC` in `T2` when I tried it in REPL.
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