How to write a singleton template?

[Li Jie]

I try to write a singleton template, but has not succeeded:

A:
template Singleton(T)
{
private T _instance;

static this()
{
_instance = new T();
}

public T instance ()
{
return _instance;
}
}

B:
template Singleton(T)
{
class Singleton
{
private static T _instance;

static this()
{
_instance = new T();
}

public static T instance ()
{
return _instance;
}
}
}

C:
template Singleton(T)
{
class Singleton
{
private static T _instance = null;

public static T instance ()
{
if (_instance == null)
_instance = new T();
return _instance;
}
}
}


// use it:

class AAA
{
public void hello ()
{
printf("hello\n");
}
}

int main(char[][] args)
{
alias Singleton!(AAA) aaa;
aaa.instance().hello();  // <== Segment fault !!!!!

return 0;
}

I want to know, how to write a singleton template?



Thanks.

- Li Jie