added async-io quiz

exercises/085_async.zig

@@ -0,0 +1,48 @@
+//
+// In previous versions of Zig, async/await used special keywords
+// like 'suspend', 'resume', and 'async' that operated on stackframes
+// directly. Those keywords no longer exist!
+//
+// Zig 0.16 replaced them with a unified I/O interface: std.Io.
+// This interface uses a VTable pattern - a struct of function pointers -
+// to abstract over different concurrency backends:
+//
+//   * Threaded  - classic thread-pool based I/O
+//   * Uring     - Linux io_uring
+//   * Kqueue    - BSD/macOS
+//   * Dispatch  - macOS Grand Central Dispatch
+//
+// The Io struct itself is tiny:
+//
+//     const Io = struct {
+//         userdata: ?*anyopaque,   // opaque state of the backend
+//         vtable: *const VTable,   // table of function pointers
+//     };
+//
+// Your code receives an Io value and calls methods on it.
+// The backend is chosen at initialization time - your code doesn't
+// need to know which one it is!
+//
+// In Zig 0.16, main() receives a std.process.Init struct to opt
+// into I/O and concurrency support:
+//
+//     pub fn main(init: std.process.Init) !void {
+//         const io = init.io;
+//         // ... use io ...
+//     }
+//
+// Let's start simple. Fix the main function to extract the Io
+// interface from init, then use it to get the current time.
+//
+const std = @import("std");
+
+pub fn main(init: std.process.Init) !void {
+    const io = init.???;
+
+    // Get the current wall-clock time using the Io interface.
+    // Hint: Timestamp.now() takes an Io and a Clock type (.real = wall clock).
+    const timestamp = std.Io.Timestamp.now(io, .real);
+
+    // Print the timestamp in seconds since the Unix epoch.
+    std.debug.print("Current time: {}s since epoch\n", .{timestamp.toSeconds()});
+}