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copied!<p>The former example, T m 0, is an example of "operator notation". Scala has three types of operator notations, prefix (called unary), infix and postfix. Let's see examples of all three in action here:</p> <pre><code>class MyByte(val n : Int) { require(n >= 0 && n <= 255) def unary_! = new MyByte(n ^ 0xff) def +(m : MyByte) = new MyByte(n + m.n) def bits = (math.log(n) / math.log(2) + 1).toInt override def toString = "0" * (8 - bits) + n.toBinaryString } </code></pre> <p>An here it is in use:</p> <pre><code>scala> val a = new MyByte(5) a: MyByte = 00000101 scala> val b = new MyByte(10) b: MyByte = 00001010 scala> ! a // Prefix/Unary res58: MyByte = 11111010 scala> a + b // Infix res59: MyByte = 00001111 scala> b bits // Postfix res60: Int = 4 </code></pre> <p>While infix and postfix notations accept any valid Scala identifier, though there is talk of restricting postfix notation, only four identifiers can be used as prefix: ~, !, - and +.</p> <p>Now, when you try "m 0", Scala discards it being a unary operator, on the grounds of not being a valid one (~, !, - and +). It finds that "m" is a valid object -- it is a function, not a method, and all functions are objects.</p> <p>As "0" is not a valid Scala identifier, it cannot be neither an infix nor a postfix operator. Therefore, Scala complains that it expected ";" -- which would separate two (almost) valid expressions: "m" and "0". If you inserted it, then it would complain that m requires either an argument, or, failing that, a "_" to turn it into a partially applied function.</p>

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