Class: Puppet::Pops::Visitor

Inherits:
Object
  • Object
show all
Defined in:
lib/puppet/pops/visitor.rb

Overview

A Visitor performs delegation to a given receiver based on the configuration of the Visitor. A new visitor is created with a given receiver, a method prefix, min, and max argument counts. e.g.

vistor = Visitor.new(self, "visit_from", 1, 1)

will make the visitor call “self.visit_from_CLASS(x)” where CLASS is resolved to the given objects class, or one of is ancestors, the first class for which there is an implementation of a method will be selected.

Raises RuntimeError if there are too few or too many arguments, or if the receiver is not configured to handle a given visiting object.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(receiver, message, min_args = 0, max_args = nil) ⇒ Visitor

Returns a new instance of Visitor.

Raises:

  • (ArgumentError) 


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# File 'lib/puppet/pops/visitor.rb', line 14

def initialize(receiver, message, min_args=0, max_args=nil)
  raise ArgumentError.new("min_args must be >= 0") if min_args < 0
  raise ArgumentError.new("max_args must be >= min_args or nil") if max_args && max_args < min_args

  @receiver = receiver
  @message = message
  @min_args = min_args
  @max_args = max_args
  @cache = Hash.new
end

Instance Attribute Details

#cache ⇒ Object (readonly) 



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# File 'lib/puppet/pops/visitor.rb', line 13

def cache
  @cache
end

#max_args ⇒ Object (readonly) 



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# File 'lib/puppet/pops/visitor.rb', line 13

def max_args
  @max_args
end

#message ⇒ Object (readonly) 



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# File 'lib/puppet/pops/visitor.rb', line 13

def message
  @message
end

#min_args ⇒ Object (readonly) 



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# File 'lib/puppet/pops/visitor.rb', line 13

def min_args
  @min_args
end

#receiver ⇒ Object (readonly) 



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# File 'lib/puppet/pops/visitor.rb', line 13

def receiver
  @receiver
end

Instance Method Details

#visit(thing, *args) ⇒ Object

Visit the configured receiver



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# File 'lib/puppet/pops/visitor.rb', line 26

def visit(thing, *args)
  visit_this(@receiver, thing, *args)
end

#visit_this(receiver, thing, *args) ⇒ Object

Visit an explicit receiver



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# File 'lib/puppet/pops/visitor.rb', line 31

def visit_this(receiver, thing, *args)
  raise "Visitor Error: Too few arguments passed. min = #{@min_args}" unless args.length >= @min_args
  if @max_args
    raise "Visitor Error: Too many arguments passed. max = #{@max_args}" unless args.length <= @max_args
  end
  if method_name = @cache[thing.class]
    return receiver.send(method_name, thing, *args)
  else
    thing.class.ancestors().each do |ancestor|
      method_name = :"#{@message}_#{ancestor.name.split("::").last}"
      # DEBUG OUTPUT
      # puts "Visitor checking: #{receiver.class}.#{method_name}, responds to: #{@receiver.respond_to? method_name}"
      next unless receiver.respond_to? method_name
      @cache[thing.class] = method_name
      return receiver.send(method_name, thing, *args)
    end
  end
  raise "Visitor Error: the configured receiver (#{receiver.class}) can't handle instance of: #{thing.class}"
end