create union enum in Zig

create_union_enum.zig

const std = @import("std");
const expect = std.testing.expect;

const cell = struct {
    v1: ?*Variant,
    v2: ?*Variant,
};

const Variant = union(enum) {
    int: i32,
    boolean: bool,
    cell: cell,

    // void can be omitted when inferring enum tag type.
    none,

    fn truthy(self: Variant) bool {
        return switch (self) {
            Variant.int => |x_int| x_int != 0,
            Variant.boolean => |x_bool| x_bool,
            Variant.cell => false,
            Variant.none => false,
        };
    }
};

test "union method" {
    var v1 = Variant{ .int = 1 };
    var v2 = Variant{ .boolean = false };

    try expect(v1.truthy());
    try expect(!v2.truthy());
}

test "create union" {
    const allocator = std.testing.allocator;

    var v1 = try allocator.create(Variant);
    defer allocator.destroy(v1);

    v1.* = .{ .int = 1 };
    try expect(v1.truthy());
}

test "create union" {
    const allocator = std.testing.allocator;

    var top = try allocator.create(Variant);
    defer allocator.destroy(top);
    top.* = .{ .cell = cell{ .v1 = null, .v2 = null } };

    var v1 = top;

    var i: i32 = 0;
    while (i < 3) : (i += 1) {
        v1.cell.v1 = try allocator.create(Variant);
        v1.cell.v1.?.* = .{ .int = i + 1 };

        var v2 = try allocator.create(Variant);
        defer allocator.destroy(v2);
        v2.* = .{ .cell = cell{ .v1 = null, .v2 = null } };
        v1.cell.v2 = v2;
        v1 = v2;
    }

    std.log.warn("{}", .{top.cell.v2.?.cell.v1}); //
}

test.log

$ zig test create_enum_union.zig 
All 2 tests passed.
$ zig version
0.10.0-dev.2880+6f0807f50