public SampleFamily plus(SampleFamily another) {
        if (this == EMPTY && another == EMPTY) {
            return SampleFamily.EMPTY;
        }
        if (this == EMPTY) {
            return another;
        }
        if (another == EMPTY) {
            return this;
        }
        return newValue(another, Double::sum);
    }
Following operations are used in DSL
oap-server/analyzer/meter-analyzer/src/main/java/org/apache/skywalking/oap/meter/analyzer/dsl/SampleFamily.java