@Override
    protected boolean equalsUnaryFunction(UnaryFunctionNode obj) {
        // "arg" checked by superclass
        String otherAttr = ((InterpolatedLookupNode)obj).getAttributeName();
        return attribute.equals(otherAttr);
    }
Sets the name of the attribute whose value we do lookup in.

@param attribute The attribute to retrieve.
@return This, to allow chaining.
searchlib/src/main/java/com/yahoo/searchlib/expression/InterpolatedLookupNode.java