using System;
class Client
{
static void Main(string[] args)
{
try{
Engine eng = Engine.GetEngine();
}catch (Exception e){
Console.WriteLine(e.Message);
}
try{
Engine eng = Engine.GetEngine();
}catch (Exception e){
Console.WriteLine(e.Message);
}
}
}
sealed class Engine
{
private static bool instanceFlag = false;
public static Engine GetEngine()
{
if (!instanceFlag)
{
instanceFlag = true;
return new Engine();
}else{
throw new Exception("An engine has already been created!");
}
}
private Engine()
{
Console.WriteLine("An Engine");
}
}
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