The name of the property or attribute for getting the
value of this argument from a gate, or a function that takes a
operation and returns this value. The later can be used to supply
a value of the serialized arg by supplying a lambda that
returns this value (i.e. lambda x: default_value)
Whether this argument is a required argument for the
default value. avoid serializing if this is the value.
Note that the DeserializingArg must also have this as default.