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# ObjectBuilder is a class to help you build Ruby-based configuration syntaxes.
# You can use it to make "builder" classes to help build particular types
# of objects, typically translating simple command-based syntax to creating
# classes and setting attributes. e.g. here is a description of a day at
# the zoo:
#
# person "Alice"
# person "Matthew"
#
# zoo("London") {
# enclosure("Butterfly House") {
#
# has_roof
# allow_visitors
#
# animals("moth", 10) {
# wings 2
# legs 2
# }
#
# animals("butterfly", 200) {
# wings 2
# legs 2
# }
# }
#
# enclosure("Aquarium") {
# no_roof
#
# animal("killer whale") {
# called "Shamu"
# wings 0
# legs 0
# tail
# }
# }
# }
#
# Here is the basic builder class for a Zoo...
#
# TODO: finish this convoluted example, if it kills me
#
class ObjectBuilder
class BuildException < StandardError; end
attr_reader :result
attr_accessor :block_result
# Generates a new builder
#
# @param [ObjectBuidler] context The level of the builder
# @param [Array] args The arguments to pass on to the builder_setup
#
def initialize(context, *args)
@context = context
@result = nil
builder_setup(*args)
end
# Generates an anonymous name
#
# @return [String]
def anonymous_name
@@sequence ||= 0 # not inherited, don't want it to be
@@sequence += 1
"anon.#{Time.now.to_i}.#{@@sequence}"
end
class << self
# Defines a new builder
#
# @param [String] word The builder's name
# @param [Class] clazz The Class the builder represents
#
# @macro [attach] is_builder
# @return The +$1+ builder.
#
# @return [NilClass]
def is_builder(word, clazz)
define_method(word.to_sym) do |*args, &block|
builder = clazz.new(*([@context] + args))
builder.instance_eval(&block) if block
["created_#{word}", "created"].each do |created_method|
created_method = created_method.to_sym
if respond_to?(created_method)
__send__(created_method, builder.result)
break
end
end
end
return nil
end
# FIXME: implement is_builder_deferred to create object at end of block?
# Defines a new block attribute
# @param [String] word The block attribute's name
# @macro [attach] is_block_attribute
# @return [NilClass] Allows use of the +$1+ word to define a block.
def is_block_attribute(word)
define_method(word.to_sym) do |*args, &block|
@result.__send__("#{word}=".to_sym, block)
end
end
# Defines a new attribute
# @param [String] word The attribute's name
# @macro [attach] is_attribute
# @return [NilClass] Allows use of the +$1+ word to set an attribute.
#
def is_attribute(word)
define_method(word.to_sym) do |*args, &block|
@result.__send__("#{word}=".to_sym, args[0])
end
end
# Defines a new boolean attribute
# @param [String] word The boolean attribute's name
# @macro [attach] is_flag_attribute
# @return [NilClass] Allows use of the +$1+ word to set an boolean attribute.
def is_flag_attribute(word)
define_method(word.to_sym) do |*args, &block|
@result.__send__("#{word}=".to_sym, true)
end
end
# Loads a new file
#
# @param [String] file
def load(file)
parse(File.read(file), file)
end
# Parses a string
#
# @param [String] string The string to parse
# @param [String] file The filename that the string was read from, for helpful error messages.
#
# @raise [BuildException] When an expected exception is raised
# @raise [NameError]
# @raise [SyntaxError]
# @raise [ArgumentError]
#
# @return [ObjectBuidler] The
def parse(string, file="string")
builder = self.new
builder.instance_eval(string, file)
builder.result
rescue NameError, NoMethodError => ex
#
# Ugh. Catch NameError and re-raise as a BuildException
#
if ex.backtrace.find{|l| l =~ /^#{file}:(\d+):/}
build_ex = BuildException.new "Unknown word `#{ex.name}' in #{file} at line #{$1}"
build_ex.set_backtrace ex.backtrace
raise build_ex
else
raise ex
end
rescue SyntaxError, ArgumentError => ex
if ex.backtrace.find{|l| l =~ /^#{file}:(\d+):/}
build_ex = BuildException.new "#{ex.message} in #{file} at line #{$1}"
build_ex.set_backtrace ex.backtrace
raise build_ex
else
raise ex
end
end
def inherited(*args)
initialize_class
end
def initialize_class
@words = {}
end
end
initialize_class
end
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