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require "bindata/base"
module BinData
# A virtual field is one that is neither read, written nor occupies space in
# the data stream. It is used to make assertions or as a convenient label
# for determining offsets or storing values.
#
# require 'bindata'
#
# class A < BinData::Record
# string :a, read_length: 5
# string :b, read_length: 5
# virtual :c, assert: -> { a == b }
# end
#
# obj = A.read("abcdeabcde")
# obj.a #=> "abcde"
# obj.c.offset #=> 10
#
# obj = A.read("abcdeABCDE") #=> BinData::ValidityError: assertion failed for obj.c
#
# == Parameters
#
# Parameters may be provided at initialisation to control the behaviour of
# an object. These params include those for BinData::Base as well as:
#
# [<tt>:assert</tt>] Raise an error when reading or assigning if the value
# of this evaluated parameter is false.
# [<tt>:value</tt>] The virtual object will always have this value.
#
class Virtual < BinData::BasePrimitive
def do_read(io)
end
def do_write(io)
end
def do_num_bytes
0.0
end
def sensible_default
nil
end
end
end
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