sumtype

A sum type for modern D.

Features

• Pattern matching, including support for introspection-based matching
• Self-referential types, using This
• Works with pure, @safe, @nogc, nothrow, and immutable
• Compatible with -betterC and -dip1000
• Zero runtime overhead compared to hand-written C
  • No heap allocation
  • Does not rely on runtime type information (TypeInfo)

Documentation

View online on Github Pages.

sumtype uses adrdox to generate its documentation. To build your own copy, run the following command from the root of the sumtype repository:

path/to/adrdox/doc2 --genSearchIndex --genSource -o generated-docs src

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.