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70 lines
2.3 KiB
Go
70 lines
2.3 KiB
Go
// The MIT License
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//
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// Copyright (c) 2020 Temporal Technologies Inc. All rights reserved.
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//
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// Copyright (c) 2020 Uber Technologies, Inc.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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package util
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import "sync"
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// A OnceCell attempts to match the semantics of Rust's `OnceCell`, but only stores strings, since that's what's needed
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// at the moment. Could be changed to use interface{} to be generic.
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type OnceCell struct {
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// Ensures we only call the fetcher one time
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once sync.Once
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// Stores the result of calling fetcher
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value string
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fetcher func() string
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}
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// Get fetches the value in the cell, calling the fetcher function if it has not yet been called
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func (oc *OnceCell) Get() string {
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oc.once.Do(func() {
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res := oc.fetcher()
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oc.value = res
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})
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return oc.value
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}
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// PopulatedOnceCell creates an already-initialized cell
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func PopulatedOnceCell(value string) OnceCell {
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return OnceCell{
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once: sync.Once{},
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value: value,
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fetcher: func() string {
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return value
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},
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}
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}
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type fetcher func() string
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// LazyOnceCell creates a cell with no initial value, the provided function will be called once and only once the first
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// time OnceCell.Get is called
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func LazyOnceCell(fetcher fetcher) OnceCell {
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return OnceCell{
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once: sync.Once{},
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value: "",
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fetcher: fetcher,
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}
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}
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