build source

vendor/k8s.io/client-go/transport/cache_go118.go

@@ -0,0 +1,46 @@
+//go:build go1.18
+
+/*
+Copyright 2022 The Kubernetes Authors.
+
+Licensed 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 transport
+
+// this is just to make the "unused" linter rule happy
+var _ = isCacheKeyComparable[tlsCacheKey]
+
+// assert at compile time that tlsCacheKey is comparable in a way that will never panic at runtime.
+//
+// Golang 1.20 introduced an exception to type constraints that allows comparable, but not
+// necessarily strictly comparable type arguments to satisfy the `comparable` type constraint,
+// thus allowing interfaces to fulfil the `comparable` constraint.
+// However, by definition, "A comparison of two interface values with identical
+// dynamic types causes a run-time panic if that type is not comparable".
+//
+// We want to make sure that comparing two `tlsCacheKey` elements won't cause a
+// runtime panic. In order to do that, we'll force the `tlsCacheKey` to be strictly
+// comparable, thus making it impossible for it to contain interfaces.
+// To assert strict comparability, we'll use another definition: "Type
+// parameters are comparable if they are strictly comparable".
+// Below, we first construct a type parameter from the `tlsCacheKey` type so that
+// we can then push this type parameter to a comparable check, thus checking these
+// are strictly comparable.
+//
+// Original suggestion from https://github.com/golang/go/issues/56548#issuecomment-1317673963
+func isCacheKeyComparable[K tlsCacheKey]() {
+	_ = isComparable[K]
+}
+
+func isComparable[T comparable]() {}