parallel_iteration.d

auto s_zip = assumeSameStructure!("g", "i", "s_prev", "f")(
                this.state.g, this.state.i, this.s_prev, this.state.f);
this.state.s = s_zip.ndMap!(z => z.g * z.i + z.s_prev * z.f).slice;

// vs

this.state.s = this.state.g.perElement!mul(this.state.i)
                        .perElement!add(this.s_prev.perElement!mul(this.state.f));
                        

// functions for the second part

auto mul ( T ) ( T a, T b ) { return a * b; }
auto add ( T ) ( T a, T b ) { return a + b; }

// Per forms per-element operation on the two vectors
auto perElement ( alias op ) ( Vector a, Vector b )
{
    auto zip = assumeSameStructure!("a", "b")(a, b);

    return zip.ndMap!(z => op(z.a, z.b)).slice;
}