@system unittest{    import std.container.binaryheap;     import std.algorithm.comparison : equal;    import std.range : take;    auto maxHeap = heapify([4, 7, 3, 1, 5]);    assert(maxHeap.take(3).equal([7, 5, 4]));     auto minHeap = heapify!"a > b"([4, 7, 3, 1, 5]);    assert(minHeap.take(3).equal([1, 3, 4]));} @system unittest{    import std.container.binaryheap;     import std.algorithm.comparison : equal;    int[] a = [ 4, 1, 3, 2, 16, 9, 10, 14, 8, 7 ];    auto h = heapify(a);    // largest element    assert(h.front == 16);    // a has the heap property    assert(equal(a, [ 16, 14, 10, 8, 7, 9, 3, 2, 4, 1 ]));} @system unittest{    import std.container.binaryheap;     import std.algorithm.comparison : equal;    import std.range : take;    int[] a = [4, 1, 3, 2, 16, 9, 10, 14, 8, 7];    auto top5 = heapify(a).take(5);    assert(top5.equal([16, 14, 10, 9, 8]));} @system unittest{    import std.container.binaryheap;     import std.conv : to;    import std.range.primitives;    {        // example from "Introduction to Algorithms" Cormen et al., p 146        int[] a = [ 4, 1, 3, 2, 16, 9, 10, 14, 8, 7 ];        auto h = heapify(a);        h = heapify!"a < b"(a);        assert(h.front == 16);        assert(a == [ 16, 14, 10, 8, 7, 9, 3, 2, 4, 1 ]);        auto witness = [ 16, 14, 10, 9, 8, 7, 4, 3, 2, 1 ];        for (; !h.empty; h.removeFront(), witness.popFront())        {            assert(!witness.empty);            assert(witness.front == h.front);        }        assert(witness.empty);    }    {        int[] a = [ 4, 1, 3, 2, 16, 9, 10, 14, 8, 7 ];        int[] b = new int[a.length];        BinaryHeap!(int[]) h = BinaryHeap!(int[])(b, 0);        foreach (e; a)        {            h.insert(e);        }        assert(b == [ 16, 14, 10, 8, 7, 3, 9, 1, 4, 2 ], to!string(b));    }} @system unittest{    import std.container.binaryheap;     import std.stdio;    import std.algorithm.comparison : equal;    import std.container.binaryheap;     int[] a = [ 4, 1, 3, 2, 16, 9, 10, 14, 8, 7 ];    auto h = heapify(a);     // Internal representation of Binary Heap tree    assert(a.equal([16, 14, 10, 8, 7, 9, 3, 2, 4, 1]));     h.replaceFront(30);    // Value 16 was replaced by 30    assert(a.equal([30, 14, 10, 8, 7, 9, 3, 2, 4, 1]));     // Making changes to the Store will be seen in the Heap    a[0] = 40;    assert(h.front() == 40);     // Inserting a new element will reallocate the Store, leaving    // the original Store unchanged.    h.insert(20);    assert(a.equal([40, 14, 10, 8, 7, 9, 3, 2, 4, 1]));     // Making changes to the original Store will not affect the Heap anymore    a[0] = 60;    assert(h.front() == 40);}