import mir.ndslice;
import mir.math.common: approxEqual;

struct PieceInterpolant
{
    int value;

    this()(int value)
    {
        this.value = value;
    }

    int opCall(uint derivative : 0, X)(int x0, int x1, X x) const
    {
        return value;
    }

    enum uint derivativeOrder = 0;
}

alias S = PieceInterpolant;
static immutable x = [0, 1, 2, 3]; // can be also an array of floating point numbers
static immutable y = [S(10), S(20), S(30)];

auto interpolant = generic(x.rcslice, y.rcslice!(const S));

assert(interpolant(-1) == 10);
assert(interpolant(0) == 10);
assert(interpolant(0.5) == 10);

assert(interpolant(1) == 20);
assert(interpolant(1.5) == 20);

assert(interpolant(2) == 30);
assert(interpolant(3) == 30);
assert(interpolant(3.4) == 30);
assert(interpolant(3) == 30);
assert(interpolant(4) == 30);