module BinData::BasePrimitive::AssertPlugin

def assert! 

def assert!
  current_value = snapshot
  expected = eval_parameter(:assert, :value => current_value)
  msg = if not expected and current_value.nil?
    "assertion failed"
  elsif not expected
    "value '#{current_value}' not as expected"
  elsif expected != true and current_value != expected
    "value is '#{current_value}' but expected '#{expected}'"
  else
    nil
  end
  raise ValidityError, "#{msg} for #{debug_name}" if msg
end

def assign(val) 

def assign(val)
  super(val)
  assert!
end

def do_read(io) #:nodoc:

:nodoc: 
def do_read(io) #:nodoc:
  super(io)
  assert!
end