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#--
# =============================================================================
# Copyright (c) 2004, Jamis Buck (jgb3@email.byu.edu)
# All rights reserved.
#
# This source file is distributed as part of the Needle dependency injection
# library for Ruby. This file (and the library as a whole) may be used only as
# allowed by either the BSD license, or the Ruby license (or, by association
# with the Ruby license, the GPL). See the "doc" subdirectory of the Needle
# distribution for the texts of these licenses.
# -----------------------------------------------------------------------------
# needle website : http://needle.rubyforge.org
# project website: http://rubyforge.org/projects/needle
# =============================================================================
#++
module Needle
module Pipeline
# The base class of instantiation pipeline elements. All subclasses
# MUST implement is the #call method, to define the logic that instances of
# that pipeline element should perform when invoked.
class Element
include Comparable
# The service definition that this element belongs to.
attr_reader :service_point
# The name of this element (may be +nil+).
attr_reader :name
# The priority of this element, used to determine ordering. Higher ordered
# elements are invoked before lower-ordered elements.
attr_reader :priority
# The hash of options that were given to this element.
attr_reader :options
# The next element in the chain. This value is only valid during pipeline
# execution--its value should not be relied upon at any other time.
attr_accessor :succ
class << self
# The default priority to use for elements of this type.
attr_reader :default_priority
# Set the default priority for elements of this type. Subclasses may
# use this method to set their default priority.
def set_default_priority( priority )
@default_priority = priority
end
end
set_default_priority 0
# Create a new element instance with the given name and priority. This
# will call #initialize_element, so that subclasses only need to
# implement that method if they have any initialization logic to perform.
def initialize( point, name=nil, priority=nil, options={} )
@service_point = point
@name, @priority = name, ( priority || self.class.default_priority )
@options = options
initialize_element
end
# Invoked by the constructor to perform any subclass-specific
# initialization logic.
def initialize_element
end
# Orders elements by their priority.
def <=>( element )
priority <=> element.priority
end
# Invoke this element's logic.
def call( *args )
raise NotImplementedError
end
# Invoked by Pipeline::Collection#reset!. Subclasses of Element that
# save any kind of state should override this method to clear that
# state on demand.
def reset!
end
alias :[] :call
end
end
end
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