@Override
            public MeterIdPrefix activeRequestPrefix(MeterRegistry registry, RequestOnlyLog log) {
                return function.apply(registry, log,
                                      MeterIdPrefixFunction.this.activeRequestPrefix(registry, log));
            }
Returns a {@link MeterIdPrefixFunction} that applies transformation on the {@link MeterIdPrefix}
returned by this function.
core/src/main/java/com/linecorp/armeria/common/metric/MeterIdPrefixFunction.java