oncepolicy

What it detects

sync.OnceFunc, sync.OnceValue, and sync.OnceValues preserve their state in the function value they return. Store that wrapper instead of constructing, calling, and discarding it in one expression.

Checks

Check	What it detects
discarded-wrapper	Reports sync.Once function wrappers that are called and immediately discarded.

Why this is flagged

Each newly created wrapper has fresh once-only state. Recreating it at every call means the wrapped work can run repeatedly, defeating the guarantee that made sync.Once useful in the first place.

Further reading: sync.OnceFunc.

How to fix it

Create the wrapper once and store the returned function in a variable or field that lives across calls. Call that stored function whenever the once-only value or action is needed.

Examples

Flagged code

func start() {
  // gohawk: sync.OnceFunc wrapper is discarded after one call
  sync.OnceFunc(initialize)()
}

Accepted code

func startOnce() {
  initializeOnce()
}