1.7 Semantics of RandomVariable objects

RandomVariable objects have value semantics. This means that they can be passed by value to functions. The can also be passed by reference to const. RandomVariables do not derive from ns3::Object and we do not use smart pointers to manage them; they are either allocated on the stack or else users explicitly manage any heap-allocated RandomVariables.

RandomVariable objects can also be used in ns-3 attributes, which means that values can be set for them through the ns-3 attribute system. An example is in the propagation models for WifiNetDevice:

TypeId
RandomPropagationDelayModel::GetTypeId (void)
{ 
  static TypeId tid = TypeId ("ns3::RandomPropagationDelayModel")
    .SetParent<PropagationDelayModel> ()
    .AddConstructor<RandomPropagationDelayModel> ()
    .AddAttribute ("Variable",
                   "The random variable which generates random delays (s).",
                   RandomVariableValue (UniformVariable (0.0, 1.0)),
         MakeRandomVariableAccessor (&RandomPropagationDelayModel::m_variable), 
                   MakeRandomVariableChecker ())
    ;
  return tid;
}

Here, the ns-3 user can change the default random variable for this delay model (which is a UniformVariable ranging from 0 to 1) through the attribute system.

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