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https://issues.apache.org/jira/browse/FLINK-6053?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16391200#comment-16391200
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ASF GitHub Bot commented on FLINK-6053:
---------------------------------------
Github user StephanEwen commented on a diff in the pull request:
https://github.com/apache/flink/pull/5501#discussion_r173146558
--- Diff:
flink-metrics/flink-metrics-core/src/main/java/org/apache/flink/metrics/StringGauge.java
---
@@ -0,0 +1,26 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.metrics;
+
+/**
+ * A StringGauge is a {@link Metric} that calculates a specific {@link
String} value at a point in time.
+ */
+public interface StringGauge extends Metric {
--- End diff --
Should be annotated with `@FunctionalInterface` to guard that this always
stays lambda-able.
Also annotate with Public / PublicEvolving?
> Gauge<T> should only take subclasses of Number, rather than everything
> ----------------------------------------------------------------------
>
> Key: FLINK-6053
> URL: https://issues.apache.org/jira/browse/FLINK-6053
> Project: Flink
> Issue Type: Improvement
> Components: Metrics
> Affects Versions: 1.2.0
> Reporter: Bowen Li
> Assignee: Chesnay Schepler
> Priority: Major
> Fix For: 1.6.0
>
>
> Currently, Flink's Gauge is defined as
> ```java
> public interface Gauge<T> extends Metric {
> T getValue();
> }
> ```
> But it doesn't make sense to have Gauge take generic types other than Number.
> And it blocks I from finishing FLINK-6013, because I cannot assume Gauge is
> only about Number. So the class should be like
> ```java
> public interface Gauge<T extends Number> extends Metric {
> T getValue();
> }
> ```
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