type FeatureSupportChecker interface {
	// Supports check if the feature is supported or not by checking internal cache.
	// By default all calls to this function before calling CheckClient returns false.
	// Returns true if all endpoints in etcd clients are supporting the feature.
	// If client A supports and client B doesn't support the feature, the `Supports` will
	// first return true at client A initializtion and then return false on client B
	// initialzation, it can flip the support at runtime.
	Supports(feature storage.Feature) bool
	// CheckClient works with etcd client to recalcualte feature support and cache it internally.
	// All etcd clients should support feature to cause `Supports` return true.
	// If client A supports and client B doesn't support the feature, the `Supports` will
	// first return true at client A initializtion and then return false on client B
	// initialzation, it can flip the support at runtime.
	CheckClient(ctx context.Context, c client, feature storage.Feature)
}

var (

	// DefaultFeatureSupportChecker is a shared global etcd FeatureSupportChecker.
	DefaultFeatureSupportChecker FeatureSupportChecker = newDefaultFeatureSupportChecker()
)