memcache/memcache.go
func Increment(c context.Context, key string, delta int64, initialValue uint64) (newValue uint64, err error) {
	return incr(c, key, delta, &initialValue)
}
func Increment(c context.Context, key string, delta int64, initialValue uint64) (newValue uint64, err error) {
	return incr(c, key, delta, &initialValue)
}
// Increment atomically increments the decimal value in the given key
// by delta and returns the new value. The value must fit in a uint64.
// Overflow wraps around, and underflow is capped to zero. The
// provided delta may be negative. If the key doesn't exist in
// memcache, the provided initial value is used to atomically
// populate it before the delta is applied.
// The key must be at most 250 bytes in length.