045_optionals.zig

//
// Sometimes you know that a variable might hold a value or
// it might not. Zig has a neat way of expressing this idea
// called Optionals. An optional type just has a '?' like this:
//
//     var foo: ?u32 = 10;
//
// Now foo can store a u32 integer OR null (a value storing
// the cosmic horror of a value NOT EXISTING!)
//
//     foo = null;
//
//     if (foo == null) beginScreaming();
//
// Before we can use the optional value as the non-null type
// (a u32 integer in this case), we need to guarantee that it
// isn't null. One way to do this is to THREATEN IT with the
// "orelse" statement.
//
//     var bar = foo orelse 2;
//
// Here, bar will either equal the u32 integer value stored in
// foo, or it will equal 2 if foo was null.
//
const std = @import("std");

pub fn main() void {
    const result = deepThought();

    // Please threaten the result so that answer is either the
    // integer value from deepThought() OR the number 42:
    var answer: u8 = result orelse 42;

    std.debug.print("The Ultimate Answer: {}.\n", .{answer});
}

fn deepThought() ?u8 {
    // It seems Deep Thought's output has declined in quality.
    // But we'll leave this as-is. Sorry Deep Thought.
    return null;
}
// Blast from the past:
//
// Optionals are a lot like error union types which can either
// hold a value or an error. Likewise, the orelse statement is
// like the catch statement used to "unwrap" a value or supply
// a default value:
//
//    var maybe_bad: Error!u32 = Error.Evil;
//    var number: u32 = maybe_bad catch 0;
//