lazy construction of an immutable object

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On Tuesday, 15 July 2014 at 15:48:10 UTC, Puming wrote:
> wow, that's interesting :-) Is it the idiomatic approach to 
> initiate immutable objects lazily? Or do people use data class 
> with immutable fields and generate a companion builder class at 
> compile time?

There's no real idiomatic approach, I think, because this is 
somewhat unexplored territory. I'd say constructing the object 
inside a pure method so it can be implicitly cast to immutable is 
more typesafe, but if you're storing the immutable reference to 
the object in a class or struct, it can only be initialized in 
that class's/struct's constructor. So the following isn't 
possible:

struct Test
{
	immutable(int*) n;
	
	private int* getPtr() pure
	{
		int* n = new int;
		*n = 42;
		
		return n;
	}
	
	public void initialize() pure
	{
		n = getPtr();
	}
}

void main()
{
	auto t = new Test();
	test.initialize();
}