Why would an initialised struct pointer field be null in the struct's destructor?

[Eduard Staniloiu via Digitalmars-d-learn]

On Saturday, 20 May 2017 at 10:48:54 UTC, Gary Willoughby wrote:
Looks like you would want to use emplace [0] here.

> 	public this(int n)
> 	{
> 		this._data = (cast(Foo*) calloc(n, Foo.sizeof))[0 .. n];
>
> 		foreach(ref element; this._data)
> 		{
> 			auto tmp = Foo(1);
> 			element = tmp;
> 		}
> 	}

Cheers,
Eduard

[0] - https://dlang.org/phobos/std_conv.html#.emplace.3