public void put(String name, Value value) {
        throw new UnsupportedOperationException(this + " does not support variable assignment");
    }
Sets a value to this, or throws an UnsupportedOperationException if
this is not supported. This default implementation does the latter.

@param name  the name of the variable to set.
@param value the value to set. Ownership of this value is transferred to this - if it is mutable
             (not frozen) it may be modified during execution
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/Context.java