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require 'bit-struct/bit-struct'
class BitStruct
# Class for nesting a BitStruct as a field within another BitStruct.
# Declared with BitStruct.nest.
class NestedField < Field
def initialize(*args)
super
end
# Used in describe.
def self.class_name
@class_name ||= "nest"
end
def class_name
@class_name ||= nested_class.name[/\w+$/]
end
def nested_class
@nested_class ||= options[:nested_class] || options["nested_class"]
end
def describe opts
if opts[:expand]
opts = opts.dup
opts[:byte_offset] = offset / 8
opts[:omit_header] = opts[:omit_footer] = true
nested_class.describe(nil, opts) {|desc| yield desc}
else
super
end
end
def add_accessors_to(cl, attr = name) # :nodoc:
unless offset % 8 == 0
raise ArgumentError,
"Bad offset, #{offset}, for nested field #{name}." +
" Must be multiple of 8."
end
unless length % 8 == 0
raise ArgumentError,
"Bad length, #{length}, for nested field #{name}." +
" Must be multiple of 8."
end
offset_byte = offset / 8
length_byte = length / 8
last_byte = offset_byte + length_byte - 1
byte_range = offset_byte..last_byte
val_byte_range = 0..length_byte-1
nc = nested_class
cl.class_eval do
define_method attr do ||
nc.new(self[byte_range])
end
define_method "#{attr}=" do |val|
if val.length != length_byte
raise ArgumentError, "Size mismatch in nested struct assignment " +
"to #{attr} with value #{val.inspect}"
end
if val.class != nc
warn "Type mismatch in nested struct assignment " +
"to #{attr} with value #{val.inspect}"
end
self[byte_range] = val[val_byte_range]
end
end
end
end
class << self
# Define a nested field in the current subclass of BitStruct,
# with the given _name_ and _nested_class_. Length is determined from
# _nested_class_.
#
# In _rest_:
#
# If a class is provided, use it for the Field class (i.e. <=NestedField).
# If a string is provided, use it for the display_name.
# If a hash is provided, use it for options.
#
# WARNING: the accessors have COPY semantics, not reference. When you call a
# reader method to get the nested structure, you get a *copy* of that data.
#
# For example:
#
# class Sub < BitStruct
# unsigned :x, 8
# end
#
# class A < BitStruct
# nest :n, Sub
# end
#
# a = A.new
#
# p a # ==> #<A n=#<Sub x=0>>
#
# # This fails to set x in a.
# a.n.x = 3
# p a # ==> #<A n=#<Sub x=0>>
#
# # This works
# n = a.n
# n.x = 3
# a.n = n
# p a # ==> #<A n=#<Sub x=3>>
#
def nest(name, nested_class, *rest)
opts = parse_options(rest, name, NestedField)
opts[:default] ||= nested_class.initial_value.dup
opts[:nested_class] = nested_class
field = add_field(name, nested_class.bit_length, opts)
field
end
alias struct nest
end
end
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