How can I use heapify in @safe code?

[klmp via Digitalmars-d-learn]

On Saturday, 1 October 2016 at 16:59:18 UTC, Burt wrote:
> Hi,
> I'd like to use a binary heap from @safe code. I thought @safe 
> is transitive

It tries too but "heapify" uses the struct "BinaryHeap" that is 
not safe at all.
(either not annotated or @safe not applicable because of what it 
uses in intern: @system stuff)

> but the following example does not compile:
>
> import std.container.binaryheap;
> @safe // This makes things fail.
> unittest
> {
> 	// Test range interface.
> 	import std.algorithm.comparison : equal;
> 	int[] a = [4, 1, 3, 2, 16, 9, 10, 14, 8, 7];
> 	auto h = heapify(a);
> 	assert(h.equal([16, 14, 10, 9, 8, 7, 4, 3, 2, 1]));
> }
>
> Is there a way to @safely call heapify? How?

No easy "good" way:
1. BinaryHeap is an old container
2. It would require to patch the standard library. So virtually 
not available before weeks (but after a quick look it doesn't 
seem possible)

There's an easy "bad" way:

import std.container.binaryheap;
@safe // This makes things fail.
unittest
{
     void foo() @trusted
     {
	    import std.algorithm.comparison : equal;
	    int[] a = [4, 1, 3, 2, 16, 9, 10, 14, 8, 7];
	    auto h = heapify(a);
	    assert(h.equal([16, 14, 10, 9, 8, 7, 4, 3, 2, 1]));
     }
}

but "bad", don't forget ;)
It's a complete cheat to trust here.