{"id":59,"date":"2011-10-04T00:38:16","date_gmt":"2011-10-04T07:38:16","guid":{"rendered":"http:\/\/www.lorrin.org\/blog\/?p=59"},"modified":"2012-03-16T23:28:10","modified_gmt":"2012-03-17T06:28:10","slug":"scalas-missing-splat-operator","status":"publish","type":"post","link":"https:\/\/www.lorrin.org\/blog\/2011\/10\/04\/scalas-missing-splat-operator\/","title":{"rendered":"Scala’s missing splat operator"},"content":{"rendered":"

Ruby, Python, and many other dynamic languages have a so-called splat operator that lets you easily invoke a function by providing a list of argument values:<\/p>\n

def f(x,y)\r\n  x*y\r\nend\r\n\r\n> fArgs = [6,7.0]\r\n=> [6, 7.0]\r\n\r\n> f(*fArgs)\r\n=> 42.0<\/pre>\n
Scala does not have a splat operator per se, but you can achieve the same effect without too much work. Sadly the syntax is different for fixed-arity<\/a> and variadic<\/a> functions.<\/p>\n
Scala splat for variadic functions<\/h3>\n
For variadic functions there effectively is a splat operator. If you invoke a variadic function and append :_*<\/code> to the argument the compiler will perform the splat:<\/p>\n
> def g(xs:Int*) = (0 \/: xs) (_ + _)\r\ng: (xs: Int*)Int\r\n\r\n> val gArgs = List(1,2,3,4)\r\ngArgs: List[Int] = List(1, 2, 3, 4)\r\n\r\n> g(gArgs:_*)\r\nres23: Int = 10<\/pre>\n
Scala splat for fixed-arity functions<\/h3>\n
> def f(x:Int, y:Double) = x * y\r\nf: (x: Int, y: Double)Double\r\n\r\n> val fArgs = (6, 7.0)\r\nfArgs: (Int, Double) = (6,7.0)\r\n\r\n> f _ tupled fArgs\r\nres8: Double = 42.0<\/pre>\n
Magic! The first part, f _<\/code>, is the syntax for a partially applied function in which none of the arguments have been specified. This works as a mechanism to get a hold of the function object. tupled<\/code> returns a new function which of arity-1 that takes a single arity-n tuple. It is defined in the Scala Function object<\/a>,<\/p>\n
However, given a List<\/em> of arguments to pass to f, I’m not sure how to easily convert the List to a Tuple.<\/p>\n
p.s. There’s a stackoverflow post about this called “scala tuple unpacking<\/a>.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Ruby, Python, and many other dynamic languages have a so-called splat operator that lets you easily invoke a function by providing a list of argument values: def f(x,y) x*y end > fArgs = [6,7.0] => [6, 7.0] > f(*fArgs) => 42.0 Scala does not have a splat operator per se, but you can achieve the […]<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[48],"tags":[18],"_links":{"self":[{"href":"https:\/\/www.lorrin.org\/blog\/wp-json\/wp\/v2\/posts\/59"}],"collection":[{"href":"https:\/\/www.lorrin.org\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.lorrin.org\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.lorrin.org\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.lorrin.org\/blog\/wp-json\/wp\/v2\/comments?post=59"}],"version-history":[{"count":7,"href":"https:\/\/www.lorrin.org\/blog\/wp-json\/wp\/v2\/posts\/59\/revisions"}],"predecessor-version":[{"id":157,"href":"https:\/\/www.lorrin.org\/blog\/wp-json\/wp\/v2\/posts\/59\/revisions\/157"}],"wp:attachment":[{"href":"https:\/\/www.lorrin.org\/blog\/wp-json\/wp\/v2\/media?parent=59"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.lorrin.org\/blog\/wp-json\/wp\/v2\/categories?post=59"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.lorrin.org\/blog\/wp-json\/wp\/v2\/tags?post=59"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}