mirror of
https://github.com/golang/go
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57 lines
930 B
Go
57 lines
930 B
Go
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// run
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// Copyright 2022 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import "fmt"
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type I interface {
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M()
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}
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type S struct {
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str string
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}
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func (s *S) M() {}
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var _ I = &S{}
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type CloningMap[K comparable, V any] struct {
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inner map[K]V
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}
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func (cm CloningMap[K, V]) With(key K, value V) CloningMap[K, V] {
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result := CloneBad(cm.inner)
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result[key] = value
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return CloningMap[K, V]{result}
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}
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func CloneBad[M ~map[K]V, K comparable, V any](m M) M {
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r := make(M, len(m))
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for k, v := range m {
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r[k] = v
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}
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return r
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}
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func main() {
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s1 := &S{"one"}
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s2 := &S{"two"}
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m := CloningMap[string, I]{inner: make(map[string]I)}
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m = m.With("a", s1)
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m = m.With("b", s2)
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it, found := m.inner["a"]
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if !found {
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panic("a not found")
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}
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if _, ok := it.(*S); !ok {
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panic(fmt.Sprintf("got %T want *main.S", it))
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}
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}
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