zig/test/behavior/optional.zig

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

test "passing an optional integer as a parameter" {
    const S = struct {
        fn entry() bool {
            var x: i32 = 1234;
            return foo(x);
        }

        fn foo(x: ?i32) bool {
            return x.? == 1234;
        }
    };
    try expect(S.entry());
    comptime try expect(S.entry());
}

test "self-referential struct through a slice of optional" {
    const S = struct {
        const Node = struct {
            children: []?Node,
            data: ?u8,

            fn new() Node {
                return Node{
                    .children = undefined,
                    .data = null,
                };
            }
        };
    };

    var n = S.Node.new();
    try expect(n.data == null);
}