50 lines
1.3 KiB
Go
50 lines
1.3 KiB
Go
package lazy
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import (
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"sync"
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)
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// Lazy holds a lazily initialized value of T.
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// Lazy non-zero lazy must not be copied after first use.
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type Lazy[T any] struct {
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once sync.Once
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m sync.RWMutex // m protects setting the value of this T
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value T // the stored value
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}
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// Get returns the value associated with this Lazy.
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//
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// If no other call to Get has started or completed an initialization, calls init to initialize the value.
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// A nil init function indicates to store the zero value of T.
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// If an initialization has been previously completed, the previously stored value is returned.
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//
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// If init panics, the initization is considered to be completed.
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// Future calls to Get() do not invoke init, and the zero value of T is returned.
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//
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// Get may safely be called concurrently.
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func (lazy *Lazy[T]) Get(init func() T) T {
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lazy.m.RLock()
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defer lazy.m.RUnlock()
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lazy.once.Do(func() {
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if init != nil {
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lazy.value = init()
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}
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})
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return lazy.value
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}
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// Set atomically sets the value of this lazy.
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// Any previously set value will be overwritten.
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// Future calls to [Get] will not invoke init.
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//
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// It may be called concurrently with calls to [Get].
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func (lazy *Lazy[T]) Set(value T) {
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lazy.m.Lock()
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defer lazy.m.Unlock()
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lazy.value = value
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lazy.once.Do(func() {})
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}
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