aphexus/sumtype

A sum type for the D programming language

sumtype

A sum type for modern D.

Features

• Pattern matching.
• Self-referential types (This).
• Full attribute correctness—pure, @safe, @nogc, and nothrow when applicable.
• No runtime dependency on TypeInfo.
• No heap allocation/boxing.

Documentation

Example

import std.math: approxEqual, cos, PI, sqrt;

struct Rectangular { double x, y; }
struct Polar { double r, theta; }
alias Vector = SumType!(Rectangular, Polar);

pure @safe @nogc nothrow
double length(Vector v)
{
    return v.match!(
        rect => sqrt(rect.x^^2 + rect.y^^2),
        polar => polar.r
    );
}

pure @safe @nogc nothrow
double horiz(Vector v)
{
    return v.match!(
        rect => rect.x,
        polar => polar.r * cos(polar.theta)
    );
}

Vector u = Rectangular(1, 1);
Vector v = Polar(1, PI/4);

assert(length(u).approxEqual(sqrt(2.0)));
assert(length(v).approxEqual(1));
assert(horiz(u).approxEqual(1));
assert(horiz(v).approxEqual(sqrt(0.5)));

Installation

If you're using dub, add the sumtype package to your project as a dependency.

Alternatively, since it's a single, self-contained module, you can simply copy sumtype.d to your source directory and compile as usual.