added ub exploration to ex090

091_async8.zig

@@ -0,0 +1,20 @@
+//
+// Perhaps you have been wondering why we have always called 'suspend'
+// with an expression in the form of an empty block:
+//
+//     suspend {}
+//
+// well,
+//
+const print = @import("std").debug.print;
+
+pub fn main() void {
+
+    var my_beef = getBeef(0);
+
+    print("beef? {X}!\n", .{my_beef});
+}
+
+fn getBeef(input: u32) u32 {
+    suspend {}
+}

exercises/090_async7.zig

@@ -35,9 +35,53 @@ pub fn main() void {
 }
 
 fn getBeef(input: u32) u32 {
-    if (input > 0xDEAD) {
+    if (input == 0xDEAD) {
         suspend {}
     }
 
     return 0xBEEF;
 }
+//
+// Going Deeper Into...
+//                     ...uNdeFiNEd beHAVi0r!
+//
+// We haven't discussed it yet, but runtime "safety" features
+// require some extra instructions in your compiled program.
+// Most of the time, you're going to want to keep these in.
+//
+// But in some programs, when data integrity is less important
+// than raw speed (some games, for example), you can compile
+// without these safety features.
+//
+// Instead of a safe panic when something goes wrong, your
+// program will now exhibit Undefined Behavior (UB), which simply
+// means that the Zig language does not (cannot) define what will
+// happen. The best case is that it will crash, but in the worst
+// case, it will continue to run with the wrong results and
+// corrupt your data or expose you to security risks.
+//
+// This program is a great way to explore UB. Once you get it
+// working, try calling the getBeef() function with the value
+// 0xDEAD so that it will invoke the 'suspend' keyword:
+//
+//     getBeef(0xDEAD)
+//
+// Now when you run the program, it will panic and give you a
+// nice stack trace to help debug the problem.
+//
+//     zig run exercises/090_async7.zig
+//     thread 328 panic: async function called...
+//     ...
+//
+// But see what happens when you turn off safety checks by using
+// ReleaseFast mode:
+//
+//     zig run -O ReleaseFast exercises/090_async7.zig
+//     beef? 0!
+//
+// This is the wrong result. On your computer, you may get a
+// different answer or it might crash! What exactly will happen
+// is UNDEFINED. Your computer is now like a wild animal,
+// reacting to bits and bytes of raw memory with the base
+// instincts of the CPU. It is both terrifying and exhilarating.
+//