Trivial subset implementation in D

README.md

Try online at: https://run.dlang.io/

subset.d

bool isSubsetOf(S1, S2)(S1 subset, S2 set)
{
    import std.algorithm : all;
    return all!(elem => elem in set)(subset[]);
}

void test(alias set)()
{
    auto s1 = set(5, 2, 1);
    auto s2 = set(3, 1, 4, 2, 5);
    import std.stdio : writefln;
    "Is { %(%s, %) } ⊆ { %(%s, %) }? %s."
        .writefln(s1[], s2[], s1.isSubsetOf(s2) ? "Yes" : "No");
}

void main()
{
    import std.container : redBlackTree;
    test!redBlackTree;
    
    static auto set(T)(T[] elems...)
    {
        struct Set
        {
            private bool[T] _data;
            alias _data this;
            auto opSlice() const { return _data.byKey; }
        }
        import std.array : assocArray;
        import std.range : repeat;
        return Set(assocArray(elems, true.repeat(elems.length)));
    }
    test!set;
}