static void Main(string[] args)
{
string key = $"this_is_key_123";
/*
* int result = 0;
* if (CustomerCache.Contains(key))
* {
* result = CustomerCache.Get<int>(key);
* }
* else
* {
* result = DataSource.Count(123);
* CustomerCache.Add(key, result);
*
* }*/
int result = CustomerCache.GetData <int>(key, () => CustomerCache.Get <int>(key));
}