ziglings/exercises/057_unions3.zig

//
// With tagged unions, it gets EVEN BETTER! If you don't have a
// need for a separate enum, you can define an inferred enum with
// your union all in one place. Just use the 'enum' keyword in
// place of the tag type:
//
//     const Foo = union(enum) {
//         small: u8,
//         medium: u32,
//         large: u64,
//     };
//
// Let's convert Insect. Doctor Zoraptera has already deleted the
// explicit InsectStat enum for you!
//
const std = @import("std");

const InsectStat = enum{ flowers_visited, still_alive };

const Insect = union(InsectStat){
  flowers_visited: u16,
  still_alive: bool,
};

pub fn main() void{
  const ant = Insect{ .still_alive = true };
  const bee = Insect{ .flowers_visited = 17 };
  
  std.debug.print("Insect report! ", .{});
  
  printInsect(ant);
  printInsect(bee);
  
  std.debug.print("\n", .{});
}

fn printInsect(insect: Insect) void{
  switch(insect){
    .still_alive => |a| std.debug.print("Ant alive is: {}. ", .{a}),
    .flowers_visited => |f| std.debug.print("Bee visited {} flowers. ", .{f}),
  }
}

// Inferred enums are neat, representing the tip of the iceberg
// in the relationship between enums and unions. You can actually
// coerce a union TO an enum (which gives you the active field
// from the union as an enum). What's even wilder is that you can
// coerce an enum to a union! But don't get too excited, that
// only works when the union type is one of those weird zero-bit
// types like void!
//
// Tagged unions, as with most ideas in computer science, have a
// long history going back to the 1960s. However, they're only
// recently becoming mainstream, particularly in system-level
// programming languages. You might have also seen them called
// "variants", "sum types", or even "enums"!