date: '2010-01-07 16:46:31' layout: post slug: scala-tip-making-it-easier-to-add-attributes-to-an-xml-element status: publish title: 'Scala tip: Making it easier to add attributes to an XML element' wordpress_id: '609' categories: Programming
In most respects Scala makes it very easy to handle XML, but there are a few things that are hard to do. One is changing the value of an existing attribute on an element, or adding a new attribute to an element.
The simplest way I found to add new attributes c="CCC" d="DDD" is to do:
val modified = elem % new UnprefixedAttribute(“c”,“CCC”,Null) % new UnprefixedAttribute(“d”,“DDD”,Null)
This is a bit verbose. What if instead you could do
val modified = elem % Map( “c”–>“CCC”, “d”–>“DDD” )
Well you can, if you add the following implicit somewhere in scope:
implicit def pimp(elem:Elem) = new { def %(attrs:Map[String,String]) = { val seq = for( (n,v) <– attrs ) yield new UnprefixedAttribute(n,v,Null) (elem /: seq) ( _ % _ ) } }
This uses the library pimping pattern discussed elsewhere to effectively add a new version of the % operator to Elem that takes a Map of attributes.
The new % operator uses a for-yield construct to convert the attrs Map into a sequence of UnprefixedAttribute objects. It then uses the /: fold operator to repeatedly apply the built-in % operator, reducing down to an element with all the attributes added.