Method: REXML::QuickPath.predicate

Defined in:

lib/rexml/quickpath.rb

.predicate(elements, path) ⇒ Object

A predicate filters a node-set with respect to an axis to produce a new node-set. For each node in the node-set to be filtered, the PredicateExpr is evaluated with that node as the context node, with the number of nodes in the node-set as the context size, and with the proximity position of the node in the node-set with respect to the axis as the context position; if PredicateExpr evaluates to true for that node, the node is included in the new node-set; otherwise, it is not included.

A PredicateExpr is evaluated by evaluating the Expr and converting the result to a boolean. If the result is a number, the result will be converted to true if the number is equal to the context position and will be converted to false otherwise; if the result is not a number, then the result will be converted as if by a call to the boolean function. Thus a location path para is equivalent to para.

# File 'lib/rexml/quickpath.rb', line 161

def QuickPath::predicate( elements, path )
  ind = 1
  bcount = 1
  while bcount > 0
    bcount += 1 if path[ind] == ?[
    bcount -= 1 if path[ind] == ?]
    ind += 1
  end
  ind -= 1
  predicate = path[1..ind-1]
  rest = path[ind+1..-1]

  # have to change 'a [=<>] b [=<>] c' into 'a [=<>] b and b [=<>] c'
  #
  predicate.gsub!(
    /#{OPERAND_}\s*([<>=])\s*#{OPERAND_}\s*([<>=])\s*#{OPERAND_}/u,
    '\1 \2 \3 and \3 \4 \5' )
  # Let's do some Ruby trickery to avoid some work:
  predicate.gsub!( /&/u, "&&" )
  predicate.gsub!( /=/u, "==" )
  predicate.gsub!( /@(\w[-\w.]*)/u, 'attribute("\1")' )
  predicate.gsub!( /\bmod\b/u, "%" )
  predicate.gsub!( /\b(\w[-\w.]*\()/u ) {
    fname = $1
    fname.gsub( /-/u, "_" )
  }

  Functions.pair = [ 0, elements.size ]
  results = []
  elements.each do |element|
    Functions.pair[0] += 1
    Functions.node = element
    res = eval( predicate )
    case res
    when true
      results << element
    when Fixnum
      results << element if Functions.pair[0] == res
    when String
      results << element
    end
  end
  return filter( results, rest )
end