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47 lines
1.9 KiB
Go
47 lines
1.9 KiB
Go
//go:build go1.18
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/*
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Copyright 2022 The Kubernetes Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package transport
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// this is just to make the "unused" linter rule happy
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var _ = isCacheKeyComparable[tlsCacheKey]
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// assert at compile time that tlsCacheKey is comparable in a way that will never panic at runtime.
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//
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// Golang 1.20 introduced an exception to type constraints that allows comparable, but not
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// necessarily strictly comparable type arguments to satisfy the `comparable` type constraint,
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// thus allowing interfaces to fulfil the `comparable` constraint.
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// However, by definition, "A comparison of two interface values with identical
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// dynamic types causes a run-time panic if that type is not comparable".
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//
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// We want to make sure that comparing two `tlsCacheKey` elements won't cause a
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// runtime panic. In order to do that, we'll force the `tlsCacheKey` to be strictly
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// comparable, thus making it impossible for it to contain interfaces.
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// To assert strict comparability, we'll use another definition: "Type
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// parameters are comparable if they are strictly comparable".
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// Below, we first construct a type parameter from the `tlsCacheKey` type so that
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// we can then push this type parameter to a comparable check, thus checking these
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// are strictly comparable.
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//
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// Original suggestion from https://github.com/golang/go/issues/56548#issuecomment-1317673963
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func isCacheKeyComparable[K tlsCacheKey]() {
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_ = isComparable[K]
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}
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func isComparable[T comparable]() {}
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