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    <p>Here's an idea:</p> <pre><code>class BiConverter[T, U, That](val toThat1: T =&gt; That, val toThat2: U =&gt; That)(implicit val num: Numeric[That]) trait LowPriorityBiConverterImplicits { implicit def subtype[A: Numeric, T &lt;: A, U &lt;: A]: BiConverter[T, U, A] = new BiConverter[T, U, A](identity, identity) } object BiConverter extends LowPriorityBiConverterImplicits { implicit def identityConverter[T: Numeric]: BiConverter[T, T, T] = new BiConverter[T, T, T](identity, identity) implicit def firstAsSecond[T, U](implicit conv: T =&gt; U, num: Numeric[U]): BiConverter[T, U, U] = new BiConverter[T, U, U](conv, identity) implicit def secondAsFirst[T, U](implicit conv: U =&gt; T, num: Numeric[T]): BiConverter[T, U, T] = new BiConverter[T, U, T](identity, conv) } class Arithmetic[T] private (A: Connector[T], B: Connector[T])(implicit n: Numeric[T]) { import Numeric.Implicits._ val sum = new Connector(A.value + B.value) } object Arithmetic { def apply[T, U, That](A: Connector[T], B: Connector[U])(implicit conv: BiConverter[T, U, That], tIsThatEvidence: T =:= That = null, uIsThatEvidence: U =:= That = null): Arithmetic[That] = { val newA: Connector[That] = if (tIsThatEvidence != null) A.asInstanceOf[Connector[That]] else new Connector(conv.toThat1(A.value)) val newB: Connector[That] = if (uIsThatEvidence != null) B.asInstanceOf[Connector[That]] else new Connector(conv.toThat2(B.value)) new Arithmetic(newA, newB)(conv.num) } } class Constant[T](var x: T) { val value = new Connector(x) } class Connector[T](f: =&gt; T) { def value: T = f override def toString = value.toString() } </code></pre> <p>Usage:</p> <pre><code>val n1 = new Constant(1) val n5 = new Constant(5) val a = Arithmetic(n1.value, n5.value) val sum1 = a.sum.value // Int println(sum1) val n55 = new Constant(5.5) val b = Arithmetic(n1.value, n55.value) val sum2 = b.sum.value // Double println(sum2) val nBig5 = new Constant(BigInt(5)) val c = Arithmetic(n1.value, nBig5.value) val sum3 = c.sum.value // BigInt println(sum3) </code></pre>
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    1. POHow to specify a generic function that works as if there is a supertype of Int, Double, etc?
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    1. USJean-Philippe Pellet
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    1. CONice :-) You cracked my problem, although the solution seems so big and "inelegant"... Anyway, thank you.
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      1. USHugo Sereno Ferreira
    2. CO:-) The solution is similar to that used in the collections framework to determine the return type of a `map` operation with the `CanBuildFrom` implicit parameter.
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      1. USJean-Philippe Pellet
    3. CO@HugoSFerreira Will you be closing the bounty with this or are you looking for another answer?
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      1. USJean-Philippe Pellet
 

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