add ex074 comptime 9

exercises/074_comptime9.zig

@@ -0,0 +1,62 @@
+//
+// In addition to knowing when to use the 'comptime' keyword,
+// it's also good to know when you DON'T need it.
+//
+// The following contexts are already IMPLICITLY evaluated at
+// compile time, and adding the 'comptime' keyword would be
+// superfluous, redundant, and smelly:
+// 
+//    * The global scope (outside of any function in a source file)
+//    * Type declarations of:
+//        * Variables
+//        * Functions (types of parameters and return values)
+//        * Structs
+//        * Unions
+//        * Enums
+//    * The test expressions in inline for and while loops
+//    * An expression passed to the @cImport() builtin
+//
+// Work with Zig for a while, and you'll start to develop and
+// intuition for these contexts. Let's work on that/ now.
+//
+// You have been given just one 'comptime' statement to use in
+// the program below. Here it is:
+//
+//     comptime
+//
+// Just one is all it takes. Use it wisely!
+//
+const print = @import("std").debug.print;
+
+// Being in the global scope, everything about this value is
+// implicitly required to be known compile time.
+const llama_count = 5;
+
+// Again, this value's type and size must be known at compile
+// time, but we're letting the compiler infer both from the
+// return type of a function.
+const llamas = makeLlamas(llama_count);
+
+// And here's the function. Note that the return value type
+// depends on one of the input arguments!
+fn makeLlamas(count: usize) [count]u8 {
+    var temp: [count]u8 = undefined;
+    var i = 0;
+
+    // Note that this does NOT need to be an inline 'while'.
+    while (i < count) : (i += 1) {
+        temp[i] = i;
+    }
+
+    return temp;
+}
+
+pub fn main() void {
+    print("My llama value is {}.\n", .{llamas[2]});
+}
+//
+// The lesson here is to not pepper your program with 'comptime'
+// keywords unless you need them. Between the implicit compile
+// time contexts and Zig's aggressive evaluation of any
+// expression it can figure out at compile time, it's sometimes
+// surprising how few places actually need the keyword.

patches/patches/074_comptime9.patch

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+42c42
+< fn makeLlamas(count: usize) [count]u8 {
+---
+> fn makeLlamas(comptime count: usize) [count]u8 {