sync.Once

Canonical guidance

• use sync.Once for shared one-time initialization
• prefer OnceValue or OnceValues when the result should be returned cleanly
• keep the initialization path simple and idempotent enough for one execution

Use when

• lazy singletons
• cached expensive setup
• shared initialization across many goroutines

Avoid

• hand-rolled boolean-plus-mutex init guards
• assuming sync.Once supports reset
• using once when eager package init would be simpler

Preferred pattern

var loadConfig = sync.OnceValue(func() Config {
	return readConfig()
})

Anti-pattern

• checking if x == nil without synchronization and then initializing from several goroutines

Explanation: This anti-pattern is tempting because it looks cheap, but it is exactly the kind of publication bug sync.Once exists to avoid.

Why

• once-based initialization is clearer and safer than open-coded lazy init races