README
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Singlet
Singlet provides threadsafe, generic singletons for Golang.
Motivation
The common pattern of using sync.Once to implement a global singleton doesn't work well when the singleton value includes a generic type, since type arguments may not be available at a global level. Singlet provides a solution, allowing you to create threadsafe, generic singletons, anywhere in your code.
Example
To use singlet, first create a Singleton. Then call GetOrDo which will create and store a value in the Singleton, if one doesn't already exist, by calling the provided func, else it will return the existing value:
var s = &singlet.Singleton{}
cache1, _ := singlet.GetOrDo(s, cache.New[int])
cache2, _ := singlet.GetOrDo(s, cache.New[int]) // cache.New is only called once
if cache1 != cache2 {
panic("caches should be equal")
}
You can also get a previously created value for a Singleton:
cache, _ := singlet.Get[*Cache[int]](singleton)
Type Mismatches
Calling Get or GetOrDo for a result type that doesn't match the previously stored result type for a Singleton will result in an ErrTypeMismatch:
singlet.GetOrDo(s, cache.New[int])
singlet.Get[string](s) // Returns ErrTypeMismatch
License
Copyright Jonathan Halterman. Released under the Apache 2.0 license.
Documentation
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Index ¶
Constants ¶
This section is empty.
Variables ¶
var ErrTypeMismatch = errors.New("the requested type does not match the singleton type")
Functions ¶
func Get ¶
Get returns a previously created value for the singleton, else the default value for T. Returns ErrTypeMismatch if the requested type does not match a type the existing singleton type. This function is threadsafe.
func GetOrDo ¶
GetOrDo will create and store a value in the Singleton, if one doesn't already exist, by calling the fn, else it will return the existing value. If the fn returns an error, that error will be returned and no value will be stored in the singleton. If the requested type does not match a type the existing singleton type, ErrTypeMismatch is returned. This function is threadsafe.
Source Files