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package ln
import (
type ctxKey int
const (
fKey ctxKey = iota
// WithF stores or appends a given F instance into a context.
func WithF(ctx context.Context, f F) context.Context {
pf, ok := FFromContext(ctx)
if !ok {
return context.WithValue(ctx, fKey, f)
return context.WithValue(ctx, fKey, pf)
// FFromContext fetches the `F` out of the context if it exists.
func FFromContext(ctx context.Context) (F, bool) {
fvp := ctx.Value(fKey)
if fvp == nil {
return nil, false
f, ok := fvp.(F)
return f, ok
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