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POHow to create a custom operator simulating dot (without parentheses)?
 

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  1. POHow to create a custom operator simulating dot (without parentheses)?
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    <p>Let's have this code:</p> <pre class="lang-scala prettyprint-override"><code>scala&gt; case class Num(n:Int){def inc = Num(n+1)} defined class Num scala&gt; implicit class Pipe(n:Num){ def | = n } defined class Pipe </code></pre> <p>This works:</p> <pre class="lang-scala prettyprint-override"><code>scala&gt; (Num(0) |) inc res7: Num = Num(1) </code></pre> <p>But is it possible to somehow (maybe implicits or macros?) make Scala to run sample bellow in a same way as the code with parentheses without modifying <code>Num</code> class?</p> <pre class="lang-scala prettyprint-override"><code>scala&gt; Num(0) | inc &lt;console&gt;:11: error: Num does not take parameters Num(0) | inc ^ </code></pre> <p>Wanted result is:</p> <pre class="lang-scala prettyprint-override"><code>scala&gt; Num(0) | inc | inc res8: Num = Num(2) </code></pre> <hr> <p>EDIT:<br> Here's code that's much closer to the real thing. I hope this is more understandable.</p> <pre><code>object ApplyTroubles2 extends App { import GrepOption.GrepOption abstract class Builder { var parent: Builder = null def getOutput: String def append(ch: Builder) = { ch.parent = this; ch } def echo(s: String) = append(new Echo(s)) def wc() = append(new Wc()) def grep(s: String, opts: Set[GrepOption]) = append(new Grep(s, opts)) def grep(s: String) = append(new Grep(s)) } object MainBuilder extends Builder { def getOutput: String = "" override def append(ch: Builder): Builder = ch } class Echo(data: String) extends Builder { def getOutput = data } class Wc() extends Builder { def getOutput = parent.getOutput.size.toString } class Grep(var pattern: String, options: Set[GrepOption]) extends Builder { def this(pattern: String) = this(pattern, Set.empty) val isCaseInsensitive = options.contains(GrepOption.CASE_INSENSITIVE) if (isCaseInsensitive) pattern = pattern.toLowerCase def getOutput = { val input = if (isCaseInsensitive) parent.getOutput.toLowerCase else parent.getOutput if (input.contains(pattern)) input else "" } } object GrepOption extends Enumeration { type GrepOption = Value val CASE_INSENSITIVE = Value } object BuilderPimps { // val wc: Builder =&gt; Builder = x =&gt; x.wc() // def echo(msg: String): Builder =&gt; Builder = x =&gt; x.echo(msg) } implicit class BuilderPimps(b: Builder) { // as suggested in one answer, should solve calling an apply method // def |(fn: Builder =&gt; Builder): Builder = fn(b) def | : Builder = b def getStringOutput: String = b.getOutput def &gt;&gt; : String = getStringOutput } import MainBuilder._ // working println(echo("xxx").wc().getOutput) println(echo("str") getStringOutput) println((echo("y") |) wc() getStringOutput) println(((((echo("y") |) echo ("zz")) |) wc()) &gt;&gt;) println(((echo("abc") |) grep ("b")) &gt;&gt;) println((echo("aBc") |) grep("AbC", Set(GrepOption.CASE_INSENSITIVE)) getStringOutput) // not working println((echo("yyyy") | wc()) getStringOutput) println(echo("yyyy") | wc() getStringOutput) println((echo("y")|) grep("y") &gt;&gt;) println(echo("x") | grep("x") | wc() &gt;&gt;) } </code></pre> <p>I realize that wanted operator adds no extra value in terms of functionality, it's supposed to be just a syntactic sugar to make things look nicer (in this case I'm trying to mimic the shell piping).</p>
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